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In commit 3D59121003721a8fad11ee72e646fd9d3076b5679c, the x86 and x86-64
<asm/param.h> was changed to include <linux/config.h> for the
configurable timer frequency.
However, asm/param.h is sometimes used in userland (it is included
indirectly from <sys/param.h>), so your commit pollutes the userland
namespace with tons of CONFIG_FOO macros. This greatly confuses
software packages (such as BusyBox) which use CONFIG_FOO macros
themselves to control the inclusion of optional features.
After a short exchange, Christoph approved this patch
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The second __const_sigaddset() should have been a sigdelset.. Compile
trouble noted by Greg K-H.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Due to incomplete memory constraints, gcc would miscompile code with
sigaddset on i386 if sig arg was const.
A quote form Jakub to make the issue clear:
"You need either
__asm__("btsl %1,%0" : "+m"(*set) : "Ir"(_sig-1) : "cc");
or
__asm__("btsl %1,%0" : "=m"(*set) : "Ir"(_sig-1), "m"(*set) : "cc");
because the btsl instruction doesn't just set the memory to some
value, but needs to read its previous content as well. If you don't
tell that fact to GCC, GCC is of course free to optimize as if the asm
was just setting the value and not depended on the previous value."
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Old code could retry for 10 seconds worst time. Only try it
for one second now.
Suggested by Yinghai Lu
Cc: Yinghai.Lu@amd.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Fields obtained through cpuid vector 0x1(ebx[16:23]) and
vector 0x4(eax[14:25], eax[26:31]) indicate the maximum values and might not
always be the same as what is available and what OS sees. So make sure
"siblings" and "cpu cores" values in /proc/cpuinfo reflect the values as seen
by OS instead of what cpuid instruction says. This will also fix the buggy BIOS
cases (for example where cpuid on a single core cpu says there are "2" siblings,
even when HT is disabled in the BIOS.
http://bugzilla.kernel.org/show_bug.cgi?id=4359)
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Introduce an atomic_inc_not_zero operation. Make this a special case of
atomic_add_unless because lockless pagecache actually wants
atomic_inc_not_negativeone due to its offset refcount.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Introduce an atomic_cmpxchg operation.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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- Make cmpxchg generally available on the i386 platform.
- Provide emulation of cmpxchg suitable for uniprocessor if built and run on
386.
From: Christoph Lameter <clameter@sgi.com>
- Cut down patch and small style changes.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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MSI hardcoded delivery mode to use logical delivery mode. Recently
x86_64 moved to use physical mode addressing to support physflat mode.
With this mode enabled noticed that my eth with MSI werent working.
msi_address_init() was hardcoded to use logical mode for i386 and x86_64.
So when we switch to use physical mode, things stopped working.
Since anyway we dont use lowest priority delivery with MSI, its always
directed to just a single CPU. Its safe and simpler to use
physical mode always, even when we use logical delivery mode for IPI's
or other ioapic RTE's.
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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Matthew Wilcox asked that this got a comment explaining why it is done
so here it is.
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
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I386 changes to track kprobe execution on a per-cpu basis. We now track the
kprobe state machine independently on each cpu, using an arch specific kprobe
control block.
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Fix more include file problems that surfaced since I submitted the previous
fix-missing-includes.patch. This should now allow not to include sched.h
from module.h, which is done by a followup patch.
Signed-off-by: Tim Schmielau <tim@physik3.uni-rostock.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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It's widely seen a MCE non-fatal error reported after resume. It seems MCE
resume is lacked under ia32. This patch tries to fix the gap.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Commit f2b36db692b7ff6972320ad9839ae656a3b0ee3e causes a bootup hang on
at least one machine. Revert for now until we understand why. The old
code may be ugly, but it works.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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__MUTEX_INITIALIZER() has no users, and equates to the more commonly used
DECLARE_MUTEX(), thus making it pretty much redundant. Remove it for good.
Signed-off-by: Arthur Othieno <a.othieno@bluewin.ch>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch removes page_pte_prot and page_pte macros from all
architectures. Some architectures define both, some only page_pte (broken)
and others none. These macros are not used anywhere.
page_pte_prot(page, prot) is identical to mk_pte(page, prot) and
page_pte(page) is identical to page_pte_prot(page, __pgprot(0)).
* The following architectures define both page_pte_prot and page_pte
arm, arm26, ia64, sh64, sparc, sparc64
* The following architectures define only page_pte (broken)
frv, i386, m32r, mips, sh, x86-64
* All other architectures define neither
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Make sure we always return, as all syscalls should. Also move the common
prototype to <linux/syscalls.h>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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All kinds of ugliness exists because we don't initialize
the apics during init_IRQs.
- We calibrate jiffies in non apic mode even when we are using apics.
- We have to have special code to initialize the apics when non-smp.
- The legacy i8259 must exist and be setup correctly, even
when we won't use it past initialization.
- The kexec on panic code must restore the state of the io_apics.
- init/main.c needs a special case for !smp smp_init on x86
In addition to pure code movement I needed a couple
of non-obvious changes:
- Move setup_boot_APIC_clock into APIC_late_time_init for
simplicity.
- Use cpu_khz to generate a better approximation of loops_per_jiffies
so I can verify the timer interrupt is working.
- Call setup_apic_nmi_watchdog again after cpu_khz is initialized on
the boot cpu.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This is platform code update for ES7000: disables IRQ overrides for the
recent ES7000 (Rascal/Zorro), cleans up the compile warning. The patch
only affects the ES7000 subarch.
Signed-off-by: <Natalie.Protasevich@unisys.com>
Acked-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add an accessor function for getting the per-CPU gdt. Callee must already
have the CPU.
Signed-off-by: Zachary Amsden <zach@vmware.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Join together some common functions (pmd_page{,_kernel}) over 2level and
3level pages.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This adjusts i386's cmpxchg patterns so that
- for word and long cmpxchg-es the compiler can utilize all possible
registers
- cmpxchg8b gets disabled when the minimum specified hardware architectur
doesn't support it (like was already happening for the byte, word, and
long ones).
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The following series implements memory hot-add for ppc64 and i386. There are
x86_64 and ia64 implementations that will be submitted shortly as well,
through the normal maintainers.
This patch:
local_mapnr is unused, except for in an alpha header. Keep the alpha one,
kill the rest.
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Convert those common loops using page_table_lock on the outside and
pte_offset_map within to use just pte_offset_map_lock within instead.
These all hold mmap_sem (some exclusively, some not), so at no level can a
page table be whipped away from beneath them. But whereas pte_alloc loops
tested with the "atomic" pmd_present, these loops are testing with pmd_none,
which on i386 PAE tests both lower and upper halves.
That's now unsafe, so add a cast into pmd_none to test only the vital lower
half: we lose a little sensitivity to a corrupt middle directory, but not
enough to worry about. It appears that i386 and UML were the only
architectures vulnerable in this way, and pgd and pud no problem.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add sem_is_read/write_locked functions to the read/write semaphores, along the
same lines of the *_is_locked spinlock functions. The swap token tuning patch
uses sem_is_read_locked; sem_is_write_locked is added for completeness.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This revised patch (as586b) makes usb-handoff permanently true and no
longer a kernel boot parameter. It also removes the piix3_usb quirk code;
that was nothing more than an early version of the USB handoff code
(written at a time when Intel's PIIX3 was about the only motherboard with
USB support). And it adds identifiers for the three PCI USB controller
classes to pci_ids.h.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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- added typedef unsigned int __nocast gfp_t;
- replaced __nocast uses for gfp flags with gfp_t - it gives exactly
the same warnings as far as sparse is concerned, doesn't change
generated code (from gcc point of view we replaced unsigned int with
typedef) and documents what's going on far better.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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include/asm/hw_irq.h:70: warning: `struct hw_interrupt_type' declared inside parameter list
include/asm/hw_irq.h:70: warning: its scope is only this definition or declaration, which is probably not what you want
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Follow up to 4732efbeb997189d9f9b04708dc26bf8613ed721 - uml must just reuse
as-is the backing architecture support. There is a micro-fixup is needed for the
included file, which won't affect i386 behaviour at all.
I've not tested compilation on x86_64, only on x86, but the code is almost the
same except the culprit test, so everything should be ok on x86_64 too.
Cc: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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As written in Documentation/feature-removal-schedule.txt, remove the
io_remap_page_range() kernel API.
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Xpress chipsets
Original patch from Bertro Simul
This is probably still not quite correct, but seems to be
the best solution so far.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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As noted by matz@suse.de
The problem is, that on i386 the syscallN
macro is defined like so:
long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \
"d" ((long)(arg3)),"S" ((long)(arg4)),"D" ((long)(arg5))); \
If one of the arguments (in the _llseek syscall it's the arg4) is a pointer
which the syscall is expected to write to (to the memory pointed to by this
ptr), then this side-effect is not captured in the asm.
If anyone uses this macro to define it's own version of the syscall
(sometimes necessary when not using glibc) and it's inlined, then GCC
doesn't know that this asm write to "*dest", when called like so for instance:
out = 1;
llseek (fd, bla, blubb, &out, trara)
use (out);
Here nobody tells GCC that "out" actually is written to (just a pointer to it
is passed to the asm). Hence GCC might (and in the above bug did)
copy-propagate "1" into the second use of "out".
The easiest solution would be to add a "memory" clobber to the definition
of this syscall macro. As this is a syscall, it shouldn't inhibit too many
optimizations.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Since this is shared code I had to implement it for i386 too
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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"extern inline" doesn't make much sense.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch (written by me and also containing many suggestions of Arjan van
de Ven) does a major cleanup of the spinlock code. It does the following
things:
- consolidates and enhances the spinlock/rwlock debugging code
- simplifies the asm/spinlock.h files
- encapsulates the raw spinlock type and moves generic spinlock
features (such as ->break_lock) into the generic code.
- cleans up the spinlock code hierarchy to get rid of the spaghetti.
Most notably there's now only a single variant of the debugging code,
located in lib/spinlock_debug.c. (previously we had one SMP debugging
variant per architecture, plus a separate generic one for UP builds)
Also, i've enhanced the rwlock debugging facility, it will now track
write-owners. There is new spinlock-owner/CPU-tracking on SMP builds too.
All locks have lockup detection now, which will work for both soft and hard
spin/rwlock lockups.
The arch-level include files now only contain the minimally necessary
subset of the spinlock code - all the rest that can be generalized now
lives in the generic headers:
include/asm-i386/spinlock_types.h | 16
include/asm-x86_64/spinlock_types.h | 16
I have also split up the various spinlock variants into separate files,
making it easier to see which does what. The new layout is:
SMP | UP
----------------------------|-----------------------------------
asm/spinlock_types_smp.h | linux/spinlock_types_up.h
linux/spinlock_types.h | linux/spinlock_types.h
asm/spinlock_smp.h | linux/spinlock_up.h
linux/spinlock_api_smp.h | linux/spinlock_api_up.h
linux/spinlock.h | linux/spinlock.h
/*
* here's the role of the various spinlock/rwlock related include files:
*
* on SMP builds:
*
* asm/spinlock_types.h: contains the raw_spinlock_t/raw_rwlock_t and the
* initializers
*
* linux/spinlock_types.h:
* defines the generic type and initializers
*
* asm/spinlock.h: contains the __raw_spin_*()/etc. lowlevel
* implementations, mostly inline assembly code
*
* (also included on UP-debug builds:)
*
* linux/spinlock_api_smp.h:
* contains the prototypes for the _spin_*() APIs.
*
* linux/spinlock.h: builds the final spin_*() APIs.
*
* on UP builds:
*
* linux/spinlock_type_up.h:
* contains the generic, simplified UP spinlock type.
* (which is an empty structure on non-debug builds)
*
* linux/spinlock_types.h:
* defines the generic type and initializers
*
* linux/spinlock_up.h:
* contains the __raw_spin_*()/etc. version of UP
* builds. (which are NOPs on non-debug, non-preempt
* builds)
*
* (included on UP-non-debug builds:)
*
* linux/spinlock_api_up.h:
* builds the _spin_*() APIs.
*
* linux/spinlock.h: builds the final spin_*() APIs.
*/
All SMP and UP architectures are converted by this patch.
arm, i386, ia64, ppc, ppc64, s390/s390x, x64 was build-tested via
crosscompilers. m32r, mips, sh, sparc, have not been tested yet, but should
be mostly fine.
From: Grant Grundler <grundler@parisc-linux.org>
Booted and lightly tested on a500-44 (64-bit, SMP kernel, dual CPU).
Builds 32-bit SMP kernel (not booted or tested). I did not try to build
non-SMP kernels. That should be trivial to fix up later if necessary.
I converted bit ops atomic_hash lock to raw_spinlock_t. Doing so avoids
some ugly nesting of linux/*.h and asm/*.h files. Those particular locks
are well tested and contained entirely inside arch specific code. I do NOT
expect any new issues to arise with them.
If someone does ever need to use debug/metrics with them, then they will
need to unravel this hairball between spinlocks, atomic ops, and bit ops
that exist only because parisc has exactly one atomic instruction: LDCW
(load and clear word).
From: "Luck, Tony" <tony.luck@intel.com>
ia64 fix
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjanv@infradead.org>
Signed-off-by: Grant Grundler <grundler@parisc-linux.org>
Cc: Matthew Wilcox <willy@debian.org>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Mikael Pettersson <mikpe@csd.uu.se>
Signed-off-by: Benoit Boissinot <benoit.boissinot@ens-lyon.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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I have a system (Biostar IDEQ210M mini-pc with a VIA chipset) which will
not reboot unless a keyboard is plugged in to it. I have tried all
combinations of the kernel "reboot=x,y" flags to no avail. Rebooting by
any method will leave the system in a wedged state (at the "Restarting
system" message).
I finally tracked the problem down to the machine's refusal to fully reboot
unless the keyboard controller status register had bit 2 set. This is the
"System flag" which when set, indicates successful completion of the
keyboard controller self-test (Basic Assurance Test, BAT).
I suppose that something is trying to protect against sporadic reboots
unless the keyboard controller is in a good state (a keyboard is present),
but I need this machine to be headless.
I found that setting the system flag (via the command byte) before giving
the "pulse reset line" command will allow the reboot to proceed. The patch
is simple, and I think it should be fine for everybody whether they have
this type of machine or not. This affects the "hard" reboot (as done when
the kernel boot flags "reboot=c,h" are used).
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Fix a typo involving CONFIG_ACPI_SRAT.
Signed-off-by: Magnus Damm <magnus@valinux.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Building asm-offsets.h has been moved to a seperate Kbuild file
located in the top-level directory. This allow us to share the
functionality across the architectures.
The old rules in architecture specific Makefiles will die
in subsequent patches.
Furhtermore the usual kbuild dependency tracking is now used
when deciding to rebuild asm-offsets.s. So we no longer risk
to fail a rebuild caused by asm-offsets.c dependencies being touched.
With this common rule-set we now force the same name across
all architectures. Following patches will fix the rest.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
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This patch gathers all the struct flock64 definitions (and the operations),
puts them under !CONFIG_64BIT and cleans up the arch files.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch just gathers together all the struct flock definitions except
xtensa into asm-generic/fcntl.h.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch puts the most popular of each fcntl operation/flag into
asm-generic/fcntl.h and cleans up the arch files.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch puts the most popular of each open flag into asm-generic/fcntl.h
and cleans up the arch files.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This set of patches creates asm-generic/fcntl.h and consolidates as much as
possible from the asm-*/fcntl.h files into it.
This patch just gathers all the identical bits of the asm-*/fcntl.h files into
asm-generic/fcntl.h.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Yoichi Yuasa <yuasa@hh.iij4u.or.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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headers
Remove the deprecated (and unused) verify_area() from various uaccess.h
headers.
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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unused and useless..
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The size of auxiliary vector is fixed at 42 in linux/sched.h. But it isn't
very obvious when looking at linux/elf.h. This patch adds AT_VECTOR_SIZE
so that we can change it if necessary when a new vector is added.
Because of include file ordering problems, doing this necessitated the
extraction of the AT_* symbols into a standalone header file.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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ATM pthread_cond_signal is unnecessarily slow, because it wakes one waiter
(which at least on UP usually means an immediate context switch to one of
the waiter threads). This waiter wakes up and after a few instructions it
attempts to acquire the cv internal lock, but that lock is still held by
the thread calling pthread_cond_signal. So it goes to sleep and eventually
the signalling thread is scheduled in, unlocks the internal lock and wakes
the waiter again.
Now, before 2003-09-21 NPTL was using FUTEX_REQUEUE in pthread_cond_signal
to avoid this performance issue, but it was removed when locks were
redesigned to the 3 state scheme (unlocked, locked uncontended, locked
contended).
Following scenario shows why simply using FUTEX_REQUEUE in
pthread_cond_signal together with using lll_mutex_unlock_force in place of
lll_mutex_unlock is not enough and probably why it has been disabled at
that time:
The number is value in cv->__data.__lock.
thr1 thr2 thr3
0 pthread_cond_wait
1 lll_mutex_lock (cv->__data.__lock)
0 lll_mutex_unlock (cv->__data.__lock)
0 lll_futex_wait (&cv->__data.__futex, futexval)
0 pthread_cond_signal
1 lll_mutex_lock (cv->__data.__lock)
1 pthread_cond_signal
2 lll_mutex_lock (cv->__data.__lock)
2 lll_futex_wait (&cv->__data.__lock, 2)
2 lll_futex_requeue (&cv->__data.__futex, 0, 1, &cv->__data.__lock)
# FUTEX_REQUEUE, not FUTEX_CMP_REQUEUE
2 lll_mutex_unlock_force (cv->__data.__lock)
0 cv->__data.__lock = 0
0 lll_futex_wake (&cv->__data.__lock, 1)
1 lll_mutex_lock (cv->__data.__lock)
0 lll_mutex_unlock (cv->__data.__lock)
# Here, lll_mutex_unlock doesn't know there are threads waiting
# on the internal cv's lock
Now, I believe it is possible to use FUTEX_REQUEUE in pthread_cond_signal,
but it will cost us not one, but 2 extra syscalls and, what's worse, one of
these extra syscalls will be done for every single waiting loop in
pthread_cond_*wait.
We would need to use lll_mutex_unlock_force in pthread_cond_signal after
requeue and lll_mutex_cond_lock in pthread_cond_*wait after lll_futex_wait.
Another alternative is to do the unlocking pthread_cond_signal needs to do
(the lock can't be unlocked before lll_futex_wake, as that is racy) in the
kernel.
I have implemented both variants, futex-requeue-glibc.patch is the first
one and futex-wake_op{,-glibc}.patch is the unlocking inside of the kernel.
The kernel interface allows userland to specify how exactly an unlocking
operation should look like (some atomic arithmetic operation with optional
constant argument and comparison of the previous futex value with another
constant).
It has been implemented just for ppc*, x86_64 and i?86, for other
architectures I'm including just a stub header which can be used as a
starting point by maintainers to write support for their arches and ATM
will just return -ENOSYS for FUTEX_WAKE_OP. The requeue patch has been
(lightly) tested just on x86_64, the wake_op patch on ppc64 kernel running
32-bit and 64-bit NPTL and x86_64 kernel running 32-bit and 64-bit NPTL.
With the following benchmark on UP x86-64 I get:
for i in nptl-orig nptl-requeue nptl-wake_op; do echo time elf/ld.so --library-path .:$i /tmp/bench; \
for j in 1 2; do echo ( time elf/ld.so --library-path .:$i /tmp/bench ) 2>&1; done; done
time elf/ld.so --library-path .:nptl-orig /tmp/bench
real 0m0.655s user 0m0.253s sys 0m0.403s
real 0m0.657s user 0m0.269s sys 0m0.388s
time elf/ld.so --library-path .:nptl-requeue /tmp/bench
real 0m0.496s user 0m0.225s sys 0m0.271s
real 0m0.531s user 0m0.242s sys 0m0.288s
time elf/ld.so --library-path .:nptl-wake_op /tmp/bench
real 0m0.380s user 0m0.176s sys 0m0.204s
real 0m0.382s user 0m0.175s sys 0m0.207s
The benchmark is at:
http://sourceware.org/ml/libc-alpha/2005-03/txt00001.txt
Older futex-requeue-glibc.patch version is at:
http://sourceware.org/ml/libc-alpha/2005-03/txt00002.txt
Older futex-wake_op-glibc.patch version is at:
http://sourceware.org/ml/libc-alpha/2005-03/txt00003.txt
Will post a new version (just x86-64 fixes so that the patch
applies against pthread_cond_signal.S) to libc-hacker ml soon.
Attached is the kernel FUTEX_WAKE_OP patch as well as a simple-minded
testcase that will not test the atomicity of the operation, but at least
check if the threads that should have been woken up are woken up and
whether the arithmetic operation in the kernel gave the expected results.
Acked-by: Ingo Molnar <mingo@redhat.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Jamie Lokier <jamie@shareable.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Yoichi Yuasa <yuasa@hh.iij4u.or.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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