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perf evsel: Don't set exclude_guest by default 

Perf tool sets exclude_guest by default while calling perf_event_open().
Because IBS does not have filtering capability, it always gets rejected
by IBS PMU driver and thus perf falls back to non-precise sampling. Fix
it by not setting exclude_guest by default on AMD.

Before:
  $ sudo ./perf record -C 0 -vvv true |& grep precise
    precise_ip                       3
  decreasing precise_ip by one (2)
    precise_ip                       2
  decreasing precise_ip by one (1)
    precise_ip                       1
  decreasing precise_ip by one (0)

After:
  $ sudo ./perf record -C 0 -vvv true |& grep precise
    precise_ip                       3
  decreasing precise_ip by one (2)
    precise_ip                       2

Committer notes:

Fixup init to zero for perf_env in older compilers:

  arch/x86/util/evsel.c:15:26: error: missing field 'os_release' initializer [-Werror,-Wmissing-field-initializers]
          struct perf_env env = {0};
                                  ^

Committer notes:

Namhyung remarked:

  It'd be nice if it can cover explicit "-e cycles:pp" as well.

Ravi clarified:

  For explicit :pp modifier, evsel->precise_max does not get set and thus perf
  does not try with different attr->precise_ip values while exclude_guest set.
  So no issue with explicit :pp:

    $ sudo ./perf record -C 0 -e cycles:pp -vvv |& grep "precise_ip\|exclude_guest"
      precise_ip                       2
      exclude_guest                    1
      precise_ip                       2
      exclude_guest                    1
    switching off exclude_guest, exclude_host
      precise_ip                       2
    ^C

  Also, with :P modifier, evsel->precise_max gets set but exclude_guest does
  not and thus :P also works fine:

    $ sudo ./perf record -C 0 -e cycles:P -vvv |& grep "precise_ip\|exclude_guest"
      precise_ip                       3
    decreasing precise_ip by one (2)
      precise_ip                       2
    ^C

Reported-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20211103072112.32312-1-ravi.bangoria@amd.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Ravi Bangoria 2021-11-02 11:01:12 +05:30 committed by Arnaldo Carvalho de Melo
parent 3500eeebed
commit eb39bf3256
3 changed files with 31 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
tools/perf/arch/x86/util/evsel.c
View File

@ -1,8 +1,31 @@
// SPDX-License-Identifier: GPL-2.0
#include <stdio.h>
#include <stdlib.h>
#include "util/evsel.h"
#include "util/env.h"
#include "linux/string.h"
void arch_evsel__set_sample_weight(struct evsel *evsel)
{
evsel__set_sample_bit(evsel, WEIGHT_STRUCT);
}
void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr)
{
struct perf_env env = { .total_mem = 0, } ;
if (!perf_env__cpuid(&env))
return;
/*
* On AMD, precise cycles event sampling internally uses IBS pmu.
* But IBS does not have filtering capabilities and perf by default
* sets exclude_guest = 1. This makes IBS pmu event init fail and
* thus perf ends up doing non-precise sampling. Avoid it by clearing
* exclude_guest.
*/
if (env.cpuid && strstarts(env.cpuid, "AuthenticAMD"))
attr->exclude_guest = 0;
free(env.cpuid);
}

12
tools/perf/util/evsel.c
View File

@ -294,7 +294,7 @@ static bool perf_event_can_profile_kernel(void)
return perf_event_paranoid_check(1);
}
struct evsel *evsel__new_cycles(bool precise, __u32 type, __u64 config)
struct evsel *evsel__new_cycles(bool precise __maybe_unused, __u32 type, __u64 config)
{
struct perf_event_attr attr = {
.type = type,
@ -305,18 +305,16 @@ struct evsel *evsel__new_cycles(bool precise, __u32 type, __u64 config)
event_attr_init(&attr);
if (!precise)
goto new_event;
/*
* Now let the usual logic to set up the perf_event_attr defaults
* to kick in when we return and before perf_evsel__open() is called.
*/
new_event:
evsel = evsel__new(&attr);
if (evsel == NULL)
goto out;
arch_evsel__fixup_new_cycles(&evsel->core.attr);
evsel->precise_max = true;
/* use asprintf() because free(evsel) assumes name is allocated */
@ -1063,6 +1061,10 @@ void __weak arch_evsel__set_sample_weight(struct evsel *evsel)
evsel__set_sample_bit(evsel, WEIGHT);
}
void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_unused)
{
}
/*
* The enable_on_exec/disabled value strategy:
*

1
tools/perf/util/evsel.h
View File

@ -283,6 +283,7 @@ void __evsel__reset_sample_bit(struct evsel *evsel, enum perf_event_sample_forma
void evsel__set_sample_id(struct evsel *evsel, bool use_sample_identifier);
void arch_evsel__set_sample_weight(struct evsel *evsel);
void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr);
int evsel__set_filter(struct evsel *evsel, const char *filter);
int evsel__append_tp_filter(struct evsel *evsel, const char *filter);