[tip:perf/urgent] perf: Fix mmap_page capabilities and docs
From: tip-bot for Peter Zijlstra
Date: Fri Mar 23 2012 - 07:35:43 EST
Commit-ID: c7206205d00ab375839bd6c7ddb247d600693c09
Gitweb: http://git.kernel.org/tip/c7206205d00ab375839bd6c7ddb247d600693c09
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 22 Mar 2012 17:26:36 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 23 Mar 2012 09:52:16 +0100
perf: Fix mmap_page capabilities and docs
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@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Vince Weaver <vweaver1@xxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Link: 1332433596.2487.33.camel@twins">http://lkml.kernel.org/r/1332433596.2487.33.camel@twins
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/cpu/perf_event.c | 10 ++++-
include/linux/perf_event.h | 83 +++++++++++++++++++++++++++++++++-----
kernel/events/core.c | 4 +-
3 files changed, 84 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 453ac94..4ef8104 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1622,6 +1622,9 @@ static int x86_pmu_event_idx(struct perf_event *event)
{
int idx = event->hw.idx;
+ if (!x86_pmu.attr_rdpmc)
+ return 0;
+
if (x86_pmu.num_counters_fixed && idx >= X86_PMC_IDX_FIXED) {
idx -= X86_PMC_IDX_FIXED;
idx |= 1 << 30;
@@ -1706,14 +1709,19 @@ static struct pmu pmu = {
.flush_branch_stack = x86_pmu_flush_branch_stack,
};
-void perf_update_user_clock(struct perf_event_mmap_page *userpg, u64 now)
+void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
{
+ userpg->cap_usr_time = 0;
+ userpg->cap_usr_rdpmc = x86_pmu.attr_rdpmc;
+ userpg->pmc_width = x86_pmu.cntval_bits;
+
if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
return;
if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
return;
+ userpg->cap_usr_time = 1;
userpg->time_mult = this_cpu_read(cyc2ns);
userpg->time_shift = CYC2NS_SCALE_FACTOR;
userpg->time_offset = this_cpu_read(cyc2ns_offset) - now;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 57ae485..ca9ed4e 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c61234b..dc3b052 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3348,7 +3348,7 @@ static void calc_timer_values(struct perf_event *event,
*running = ctx_time - event->tstamp_running;
}
-void __weak perf_update_user_clock(struct perf_event_mmap_page *userpg, u64 now)
+void __weak arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
{
}
@@ -3398,7 +3398,7 @@ void perf_event_update_userpage(struct perf_event *event)
userpg->time_running = running +
atomic64_read(&event->child_total_time_running);
- perf_update_user_clock(userpg, now);
+ arch_perf_update_userpage(userpg, now);
barrier();
++userpg->lock;
--
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