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perf: Fix mmap_page capabilities and docs

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Complete the syscall-less self-profiling feature and address
all complaints, namely:

 - capabilities, so we can detect what is actually available at runtime

     Add a capabilities field to perf_event_mmap_page to indicate
     what is actually available for use.

 - on x86: RDPMC weirdness due to being 40/48 bits and not sign-extending
   properly.

 - ABI documentation as to how all this stuff works.

Also improve the documentation for the new features.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vince Weaver <vweaver1@eecs.utk.edu>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1332433596.2487.33.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2012-03-22 17:26:36 +01:00 • committed by Ingo Molnar
parent c5bc437702
commit c7206205d0
3 changed files with 84 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

83
include/linux/perf_event.h
View file

@ -299,18 +299,31 @@ struct perf_event_mmap_page {
/*
* Bits needed to read the hw events in user-space.
*
* u32 seq;
* s64 count;
* u32 seq, time_mult, time_shift, idx, width;
* u64 count, enabled, running;
* u64 cyc, time_offset;
* s64 pmc = 0;
*
* do {
* seq = pc->lock;
*
* barrier()
* if (pc->index) {
* count = pmc_read(pc->index - 1);
* count += pc->offset;
* } else
* goto regular_read;
*
* enabled = pc->time_enabled;
* running = pc->time_running;
*
* if (pc->cap_usr_time && enabled != running) {
* cyc = rdtsc();
* time_offset = pc->time_offset;
* time_mult = pc->time_mult;
* time_shift = pc->time_shift;
* }
*
* idx = pc->index;
* count = pc->offset;
* if (pc->cap_usr_rdpmc && idx) {
* width = pc->pmc_width;
* pmc = rdpmc(idx - 1);
* }
*
* barrier();
* } while (pc->lock != seq);
@ -323,14 +336,57 @@ struct perf_event_mmap_page {
__s64 offset; /* add to hardware event value */
__u64 time_enabled; /* time event active */
__u64 time_running; /* time event on cpu */
__u32 time_mult, time_shift;
union {
__u64 capabilities;
__u64 cap_usr_time : 1,
cap_usr_rdpmc : 1,
cap_____res : 62;
};
/*
* If cap_usr_rdpmc this field provides the bit-width of the value
* read using the rdpmc() or equivalent instruction. This can be used
* to sign extend the result like:
*
* pmc <<= 64 - width;
* pmc >>= 64 - width; // signed shift right
* count += pmc;
*/
__u16 pmc_width;
/*
* If cap_usr_time the below fields can be used to compute the time
* delta since time_enabled (in ns) using rdtsc or similar.
*
* u64 quot, rem;
* u64 delta;
*
* quot = (cyc >> time_shift);
* rem = cyc & ((1 << time_shift) - 1);
* delta = time_offset + quot * time_mult +
* ((rem * time_mult) >> time_shift);
*
* Where time_offset,time_mult,time_shift and cyc are read in the
* seqcount loop described above. This delta can then be added to
* enabled and possible running (if idx), improving the scaling:
*
* enabled += delta;
* if (idx)
* running += delta;
*
* quot = count / running;
* rem = count % running;
* count = quot * enabled + (rem * enabled) / running;
*/
__u16 time_shift;
__u32 time_mult;
__u64 time_offset;
/*
* Hole for extension of the self monitor capabilities
*/
__u64 __reserved[121]; /* align to 1k */
__u64 __reserved[120]; /* align to 1k */
/*
* Control data for the mmap() data buffer.
@ -347,6 +403,13 @@ struct perf_event_mmap_page {
__u64 data_tail; /* user-space written tail */
};
/*
* Build time assertion that we keep the data_head at the intended location.
* IOW, validation we got the __reserved[] size right.
*/
extern char __assert_mmap_data_head_offset
[1 - 2*!!(offsetof(struct perf_event_mmap_page, data_head) != 1024)];
#define PERF_RECORD_MISC_CPUMODE_MASK (7 << 0)
#define PERF_RECORD_MISC_CPUMODE_UNKNOWN (0 << 0)
#define PERF_RECORD_MISC_KERNEL (1 << 0)