From 37d81828385f8ff823caaaf1a83e72d065b6cfa1 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Mon, 23 Mar 2009 18:22:08 +0100 Subject: perf_counter: add an mmap method to allow userspace to read hardware counters Impact: new feature giving performance improvement This adds the ability for userspace to do an mmap on a hardware counter fd and get access to a read-only page that contains the information needed to translate a hardware counter value to the full 64-bit counter value that would be returned by a read on the fd. This is useful on architectures that allow user programs to read the hardware counters, such as PowerPC. The mmap will only succeed if the counter is a hardware counter monitoring the current process. On my quad 2.5GHz PowerPC 970MP machine, userspace can read a counter and translate it to the full 64-bit value in about 30ns using the mmapped page, compared to about 830ns for the read syscall on the counter, so this does give a significant performance improvement. Signed-off-by: Paul Mackerras Signed-off-by: Peter Zijlstra Orig-LKML-Reference: <20090323172417.297057964@chello.nl> Signed-off-by: Ingo Molnar --- include/linux/perf_counter.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include') diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index 18dc17d0a61..40b324e91bf 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -143,6 +143,17 @@ struct perf_counter_hw_event { #define PERF_COUNTER_IOC_ENABLE _IO('$', 0) #define PERF_COUNTER_IOC_DISABLE _IO('$', 1) +/* + * Structure of the page that can be mapped via mmap + */ +struct perf_counter_mmap_page { + __u32 version; /* version number of this structure */ + __u32 compat_version; /* lowest version this is compat with */ + __u32 lock; /* seqlock for synchronization */ + __u32 index; /* hardware counter identifier */ + __s64 offset; /* add to hardware counter value */ +}; + #ifdef __KERNEL__ /* * Kernel-internal data types and definitions: @@ -278,6 +289,9 @@ struct perf_counter { int oncpu; int cpu; + /* pointer to page shared with userspace via mmap */ + unsigned long user_page; + /* read() / irq related data */ wait_queue_head_t waitq; /* optional: for NMIs */ @@ -361,6 +375,7 @@ extern int perf_counter_task_enable(void); extern int hw_perf_group_sched_in(struct perf_counter *group_leader, struct perf_cpu_context *cpuctx, struct perf_counter_context *ctx, int cpu); +extern void perf_counter_update_userpage(struct perf_counter *counter); extern void perf_counter_output(struct perf_counter *counter, int nmi, struct pt_regs *regs); -- cgit v1.2.3