Commit eb39bf32 authored by Ravi Bangoria's avatar Ravi Bangoria Committed by Arnaldo Carvalho de Melo
Browse files

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: default avatarKim Phillips <kim.phillips@amd.com>
Signed-off-by: default avatarRavi Bangoria <ravi.bangoria@amd.com>
Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
Tested-by: default avatarArnaldo 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 3500eeeb

tools/perf/arch/x86/util/evsel.c

+23 −0
Original line number Diff line number Diff line 
// 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);

}

tools/perf/util/evsel.c

+7 −5
Original line number Diff line number Diff line
@@ -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:

 *

tools/perf/util/evsel.h

+1 −0
Original line number Diff line number Diff line
@@ -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);