aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/xen
AgeCommit message (Collapse)Author
2008-10-12Merge branch 'linus' into x86/xenIngo Molnar
Conflicts: arch/x86/kernel/cpu/common.c arch/x86/kernel/process_64.c arch/x86/xen/enlighten.c
2008-10-11Merge branch 'x86/apic' into x86-v28-for-linus-phase4-BIngo Molnar
Conflicts: arch/x86/kernel/apic_32.c arch/x86/kernel/apic_64.c arch/x86/kernel/setup.c drivers/pci/intel-iommu.c include/asm-x86/cpufeature.h include/asm-x86/dma-mapping.h
2008-10-10xen: do not reserve 2 pages of padding between hypervisor and fixmap.Ian Campbell
When reserving space for the hypervisor the Xen paravirt backend adds an extra two pages (this was carried forward from the 2.6.18-xen tree which had them "for safety"). Depending on various CONFIG options this can cause the boot time fixmaps to span multiple PMDs which is not supported and triggers a WARN in early_ioremap_init(). This was exposed by 2216d199b1430d1c0affb1498a9ebdbd9c0de439 which moved the dmi table parsing earlier. x86: fix CONFIG_X86_RESERVE_LOW_64K=y The bad_bios_dmi_table() quirk never triggered because we do DMI setup too late. Move it a bit earlier. There is no real reason to reserve these two extra pages and the fixmap already incorporates FIX_HOLE which serves the same purpose. None of the other callers of reserve_top_address do this. Signed-off-by: Ian Campbell <ian.campbell@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-09xen: use spin_lock_nest_lock when pinning a pagetableJeremy Fitzhardinge
When pinning/unpinning a pagetable with split pte locks, we can end up holding multiple pte locks at once (we need to hold the locks while there's a pending batched hypercall affecting the pte page). Because all the pte locks are in the same lock class, lockdep thinks that we're potentially taking a lock recursively. This warning is spurious because we always take the pte locks while holding mm->page_table_lock. lockdep now has spin_lock_nest_lock to express this kind of dominant lock use, so use it here so that lockdep knows what's going on. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-06Merge branches 'x86/alternatives', 'x86/cleanups', 'x86/commandline', ↵Ingo Molnar
'x86/crashdump', 'x86/debug', 'x86/defconfig', 'x86/doc', 'x86/exports', 'x86/fpu', 'x86/gart', 'x86/idle', 'x86/mm', 'x86/mtrr', 'x86/nmi-watchdog', 'x86/oprofile', 'x86/paravirt', 'x86/reboot', 'x86/sparse-fixes', 'x86/tsc', 'x86/urgent' and 'x86/vmalloc' into x86-v28-for-linus-phase1
2008-10-03xen: clean up x86-64 warningsJeremy Fitzhardinge
There are a couple of Xen features which rely on directly accessing per-cpu data via a segment register, which is not yet available on x86-64. In the meantime, just disable direct access to the vcpu info structure; this leaves some of the code as dead, but it will come to life in time, and the warnings are suppressed. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-30xen: make CONFIG_XEN_SAVE_RESTORE depend on CONFIG_XENChuck Ebbert
Xen options need to depend on XEN. Also, add newline at end of file. Without this patch you need to disable CONFIG_PM in order to disable CPU hotplugging. Signed-off-by: Chuck Ebbert <cebbert@redhat.com> Acked-by Jeremy Fitzhardinge <jeremy@goop.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-23Merge branch 'timers/urgent' into x86/xenIngo Molnar
Conflicts: arch/x86/kernel/process_32.c arch/x86/kernel/process_64.c Manual merge: arch/x86/kernel/smpboot.c Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-14xen: fix for xen guest with mem > 3.7GJeremy Fitzhardinge
PFN_PHYS() can truncate large addresses unless its passed a suitable large type. This is fixed more generally in the patch series introducing phys_addr_t, but we need a short-term fix to solve a Xen regression reported by Roberto De Ioris. Reported-by: Roberto De Ioris <roberto@unbit.it> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-10xen: fix pinning when not using split pte locksJeremy Fitzhardinge
We only pin PTE pages when using split PTE locks, so don't do the pin/unpin when attaching/detaching pte pages to a pinned pagetable. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-10Merge branch 'core/xen' into x86/xenIngo Molnar
2008-09-10mm: define USE_SPLIT_PTLOCKS rather than repeating expressionJeremy Fitzhardinge
Define USE_SPLIT_PTLOCKS as a constant expression rather than repeating "NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS" all over the place. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Acked-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-08xen: make CPU hotplug functions staticAlex Nixon
There's no need for these functions to be accessed from outside of xen/smp.c Signed-off-by: Alex Nixon <alex.nixon@citrix.com> Acked-by: Jeremy Fitzhardinge <jeremy@goop.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-08x86, xen: fix build when !CONFIG_HOTPLUG_CPUAlex Nixon
Signed-off-by: Alex Nixon <alex.nixon@citrix.com> Acked-by: Jeremy Fitzhardinge <jeremy@goop.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-06x86, xen: Use native_pte_flags instead of native_pte_val for .pte_flagsEduardo Habkost
Using native_pte_val triggers the BUG_ON() in the paravirt_ops version of pte_flags(). Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-25xen: implement CPU hotpluggingAlex Nixon
Note the changes from 2.6.18-xen CPU hotplugging: A vcpu_down request from the remote admin via Xenbus both hotunplugs the CPU, and disables it by removing it from the cpu_present map, and removing its entry in /sys. A vcpu_up request from the remote admin only re-enables the CPU, and does not immediately bring the CPU up. A udev event is emitted, which can be caught by the user if he wishes to automatically re-up CPUs when available, or implement a more complex policy. Signed-off-by: Alex Nixon <alex.nixon@citrix.com> Acked-by: Jeremy Fitzhardinge <jeremy@goop.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-22x86: build fix in "xen spinlock updates and performance measurements"Jeremy Fitzhardinge
Ingo Molnar wrote: > -tip testing found this build failure: > > arch/x86/xen/spinlock.c: In function ‘spin_time_start’: > arch/x86/xen/spinlock.c:60: error: implicit declaration of function ‘xen_clocksource_read’ > > i've excluded these new commits for now from tip/master - could you > please send a delta fix against tip/x86/xen? Make xen_clocksource_read non-static. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-22x86, paravirt_ops: use unsigned long instead of u32 for alloc_p*() pfn argsEduardo Habkost
This patch changes the pfn args from 'u32' to 'unsigned long' on alloc_p*() functions on paravirt_ops, and the corresponding implementations for Xen and VMI. The prototypes for CONFIG_PARAVIRT=n are already using unsigned long, so paravirt.h now matches the prototypes on asm-x86/pgalloc.h. It shouldn't result in any changes on generated code on 32-bit, with or without CONFIG_PARAVIRT. On both cases, 'codiff -f' didn't show any change after applying this patch. On 64-bit, there are (expected) binary changes only when CONFIG_PARAVIRT is enabled, as the patch is really supposed to change the size of the pfn args. [ v2: KVM_GUEST: use the right parameter type on kvm_release_pt() ] Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Acked-by: Jeremy Fitzhardinge <jeremy@goop.org> Acked-by: Zachary Amsden <zach@vmware.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-21xen: measure how long spinlocks spend blockingJeremy Fitzhardinge
Measure how long spinlocks spend blocked. Also rename some fields to be more consistent. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Acked-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-21xen: allow interrupts to be enabled while doing a blocking spinJeremy Fitzhardinge
If spin_lock is called in an interrupts-enabled context, we can safely enable interrupts while spinning. We don't bother for the actual spin loop, but if we timeout and fall back to blocking, it's definitely worthwhile enabling interrupts if possible. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Acked-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-21xen: add debugfs supportJeremy Fitzhardinge
Add support for exporting statistics on mmu updates, multicall batching and pv spinlocks into debugfs. The base path is xen/ and each subsystem adds its own directory: mmu, multicalls, spinlocks. In each directory, writing 1 to "zero_stats" will cause the corresponding stats to be zeroed the next time they're updated. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Acked-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-21xen: save previous spinlock when blockingJeremy Fitzhardinge
A spinlock can be interrupted while spinning, so make sure we preserve the previous lock of interest if we're taking a lock from within an interrupt handler. We also need to deal with the case where the blocking path gets interrupted between testing to see if the lock is free and actually blocking. If we get interrupted there and end up in the state where the lock is free but the irq isn't pending, then we'll block indefinitely in the hypervisor. This fix is to make sure that any nested lock-takers will always leave the irq pending if there's any chance the outer lock became free. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Acked-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-20xen: add xen_ prefixes to make tracing with ftrace easierJeremy Fitzhardinge
It's easier to pattern match on Xen function if they all start with xen_. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-20xen: clarify locking used when pinning a pagetable.Jeremy Fitzhardinge
Add some comments explaining the locking and pinning algorithm when using split pte locks. Also implement a minor optimisation of not pinning the PTE when not using split pte locks. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Xen-devel <xen-devel@lists.xensource.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-20xen: clean up domain mode predicatesJeremy Fitzhardinge
There are four operating modes Xen code may find itself running in: - native - hvm domain - pv dom0 - pv domU Clean up predicates for testing for these states to make them more consistent. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Xen-devel <xen-devel@lists.xensource.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-31xen_alloc_ptpage: cast PFN_PHYS() argument to unsigned longEduardo Habkost
Currently paravirt_ops alloc_p*() uses u32 for the pfn args. We should change that later, but while the pfn parameter is still u32, we need to cast the PFN_PHYS() argument at xen_alloc_ptpage() to unsigned long, otherwise it will lose bits on the shift. I think PFN_PHYS() should behave better when fed with smaller integers, but a cast to unsigned long won't be enough for all cases on 32-bit PAE, and a cast to u64 would be overkill for most users of PFN_PHYS(). We could have two different flavors of PFN_PHYS: one for low pages only (unsigned long) and another that works for any page (u64)), but while we don't have it, we will need the cast to unsigned long on xen_alloc_ptpage(). Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-31xen: fix allocation and use of large ldts, cleanupJeremy Fitzhardinge
Add a proper comment for set_aliased_prot() and fix an unsigned long/void * warning. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-31xen: compile irq functions without -pg for ftraceJeremy Fitzhardinge
For some reason I managed to miss a bunch of irq-related functions which also need to be compiled without -pg when using ftrace. This patch moves them into their own file, and starts a cleanup process I've been meaning to do anyway. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Sam Ravnborg <sam@ravnborg.org> Cc: "Alex Nixon (Intern)" <Alex.Nixon@eu.citrix.com> Cc: Eduardo Habkost <ehabkost@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-31Merge branch 'x86/spinlocks' into x86/xenIngo Molnar
2008-07-28xen: suppress known wrmsrsJeremy Fitzhardinge
In general, Xen doesn't support wrmsr from an unprivileged domain; it just ends up ignoring the instruction and printing a message on the console. Given that there are sets of MSRs we know the kernel will try to write to, but we don't care, just eat them in xen_write_msr to cut down on console noise. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-28xen: fix allocation and use of large ldtsJeremy Fitzhardinge
When the ldt gets to more than 1 page in size, the kernel uses vmalloc to allocate it. This means that: - when making the ldt RO, we must update the pages in both the vmalloc mapping and the linear mapping to make sure there are no RW aliases. - we need to use arbitrary_virt_to_machine to compute the machine addr for each update Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-26x86, xen: Use native_pte_flags instead of native_pte_val for .pte_flagsEduardo Habkost
Using native_pte_val triggers the BUG_ON() in the paravirt_ops version of pte_flags(). Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-26Merge branch 'linus' into x86/xenIngo Molnar
2008-07-25Merge branch 'linus' into x86/x2apicIngo Molnar
Conflicts: drivers/pci/dmar.c Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-24x86: split spinlock implementations out into their own filesJeremy Fitzhardinge
ftrace requires certain low-level code, like spinlocks and timestamps, to be compiled without -pg in order to avoid infinite recursion. This patch splits out the core paravirt spinlocks and the Xen spinlocks into separate files which can be compiled without -pg. Also do xen/time.c while we're about it. As a result, we can now use ftrace within a Xen domain. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-24x86/paravirt/xen: properly fill out the ldt opsJeremy Fitzhardinge
LTP testing showed that Xen does not properly implement sys_modify_ldt(). This patch does the final little bits needed to make the ldt work properly. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-24xen: don't use sysret for sysexit32Jeremy Fitzhardinge
When implementing sysexit32, don't let Xen use sysret to return to userspace. That results in usermode register state being trashed. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Mark McLoughlin <markmc@redhat.com> Cc: Eduardo Habkost <ehabkost@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-23Merge branch 'cpus4096-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'cpus4096-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (31 commits) NR_CPUS: Replace NR_CPUS in speedstep-centrino.c cpumask: Provide a generic set of CPUMASK_ALLOC macros, FIXUP NR_CPUS: Replace NR_CPUS in cpufreq userspace routines NR_CPUS: Replace per_cpu(..., smp_processor_id()) with __get_cpu_var NR_CPUS: Replace NR_CPUS in arch/x86/kernel/genapic_flat_64.c NR_CPUS: Replace NR_CPUS in arch/x86/kernel/genx2apic_uv_x.c NR_CPUS: Replace NR_CPUS in arch/x86/kernel/cpu/proc.c NR_CPUS: Replace NR_CPUS in arch/x86/kernel/cpu/mcheck/mce_64.c cpumask: Optimize cpumask_of_cpu in lib/smp_processor_id.c, fix cpumask: Use optimized CPUMASK_ALLOC macros in the centrino_target cpumask: Provide a generic set of CPUMASK_ALLOC macros cpumask: Optimize cpumask_of_cpu in lib/smp_processor_id.c cpumask: Optimize cpumask_of_cpu in kernel/time/tick-common.c cpumask: Optimize cpumask_of_cpu in drivers/misc/sgi-xp/xpc_main.c cpumask: Optimize cpumask_of_cpu in arch/x86/kernel/ldt.c cpumask: Optimize cpumask_of_cpu in arch/x86/kernel/io_apic_64.c cpumask: Replace cpumask_of_cpu with cpumask_of_cpu_ptr Revert "cpumask: introduce new APIs" cpumask: make for_each_cpu_mask a bit smaller net: Pass reference to cpumask variable in net/sunrpc/svc.c ... Fix up trivial conflicts in drivers/cpufreq/cpufreq.c manually
2008-07-22x86: add PTE_FLAGS_MASKJeremy Fitzhardinge
PTE_PFN_MASK was getting lonely, so I made it a friend. Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-22x86: rename PTE_MASK to PTE_PFN_MASKJeremy Fitzhardinge
Rusty, in his peevish way, complained that macros defining constants should have a name which somewhat accurately reflects the actual purpose of the constant. Aside from the fact that PTE_MASK gives no clue as to what's actually being masked, and is misleadingly similar to the functionally entirely different PMD_MASK, PUD_MASK and PGD_MASK, I don't really see what the problem is. But if this patch silences the incessent noise, then it will have achieved its goal (TODO: write test-case). Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-22Merge branch 'linus' into x86/x2apicIngo Molnar
2008-07-21Merge branch 'x86/paravirt-spinlocks' into x86/for-linusIngo Molnar
2008-07-21Merge branches 'x86/urgent', 'x86/amd-iommu', 'x86/apic', 'x86/cleanups', ↵Ingo Molnar
'x86/core', 'x86/cpu', 'x86/fixmap', 'x86/gart', 'x86/kprobes', 'x86/memtest', 'x86/modules', 'x86/nmi', 'x86/pat', 'x86/reboot', 'x86/setup', 'x86/step', 'x86/unify-pci', 'x86/uv', 'x86/xen' and 'xen-64bit' into x86/for-linus
2008-07-20x86, xen: fix apic_ops build on UPIngo Molnar
fix: arch/x86/xen/enlighten.c:615: error: variable ‘xen_basic_apic_ops’ has initializer but incomplete type arch/x86/xen/enlighten.c:616: error: unknown field ‘read’ specified in initializer [...] Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-18Merge branch 'x86/apic' into x86/x2apicIngo Molnar
Conflicts: arch/x86/kernel/paravirt.c arch/x86/kernel/smpboot.c arch/x86/kernel/vmi_32.c arch/x86/lguest/boot.c arch/x86/xen/enlighten.c include/asm-x86/apic.h include/asm-x86/paravirt.h Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-18Merge branch 'linus' into x86/x2apicIngo Molnar
2008-07-18xen: report hypervisor versionJeremy Fitzhardinge
Various versions of the hypervisor have differences in what ABIs and features they support. Print some details into the boot log to help with remote debugging. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-18x86: APIC: remove apic_write_around(); use alternativesMaciej W. Rozycki
Use alternatives to select the workaround for the 11AP Pentium erratum for the affected steppings on the fly rather than build time. Remove the X86_GOOD_APIC configuration option and replace all the calls to apic_write_around() with plain apic_write(), protecting accesses to the ESR as appropriate due to the 3AP Pentium erratum. Remove apic_read_around() and all its invocations altogether as not needed. Remove apic_write_atomic() and all its implementing backends. The use of ASM_OUTPUT2() is not strictly needed for input constraints, but I have used it for readability's sake. I had the feeling no one else was brave enough to do it, so I went ahead and here it is. Verified by checking the generated assembly and tested with both a 32-bit and a 64-bit configuration, also with the 11AP "feature" forced on and verified with gdb on /proc/kcore to work as expected (as an 11AP machines are quite hard to get hands on these days). Some script complained about the use of "volatile", but apic_write() needs it for the same reason and is effectively a replacement for writel(), so I have disregarded it. I am not sure what the policy wrt defconfig files is, they are generated and there is risk of a conflict resulting from an unrelated change, so I have left changes to them out. The option will get removed from them at the next run. Some testing with machines other than mine will be needed to avoid some stupid mistake, but despite its volume, the change is not really that intrusive, so I am fairly confident that because it works for me, it will everywhere. Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-17x86, xen, power: fix up config dependencies on PMJeremy Fitzhardinge
Xen save/restore needs bits of code enabled by PM_SLEEP, and PM_SLEEP depends on PM. So make XEN_SAVE_RESTORE depend on PM and PM_SLEEP depend on XEN_SAVE_RESTORE. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Acked-by: Rafael J. Wysocki <rjw@sisk.pl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-16xen: implement Xen-specific spinlocksJeremy Fitzhardinge
The standard ticket spinlocks are very expensive in a virtual environment, because their performance depends on Xen's scheduler giving vcpus time in the order that they're supposed to take the spinlock. This implements a Xen-specific spinlock, which should be much more efficient. The fast-path is essentially the old Linux-x86 locks, using a single lock byte. The locker decrements the byte; if the result is 0, then they have the lock. If the lock is negative, then locker must spin until the lock is positive again. When there's contention, the locker spin for 2^16[*] iterations waiting to get the lock. If it fails to get the lock in that time, it adds itself to the contention count in the lock and blocks on a per-cpu event channel. When unlocking the spinlock, the locker looks to see if there's anyone blocked waiting for the lock by checking for a non-zero waiter count. If there's a waiter, it traverses the per-cpu "lock_spinners" variable, which contains which lock each CPU is waiting on. It picks one CPU waiting on the lock and sends it an event to wake it up. This allows efficient fast-path spinlock operation, while allowing spinning vcpus to give up their processor time while waiting for a contended lock. [*] 2^16 iterations is threshold at which 98% locks have been taken according to Thomas Friebel's Xen Summit talk "Preventing Guests from Spinning Around". Therefore, we'd expect the lock and unlock slow paths will only be entered 2% of the time. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Christoph Lameter <clameter@linux-foundation.org> Cc: Petr Tesarik <ptesarik@suse.cz> Cc: Virtualization <virtualization@lists.linux-foundation.org> Cc: Xen devel <xen-devel@lists.xensource.com> Cc: Thomas Friebel <thomas.friebel@amd.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>