eb39bf3256
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>
31 lines
813 B
C
31 lines
813 B
C
// SPDX-License-Identifier: GPL-2.0
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#include <stdio.h>
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#include <stdlib.h>
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#include "util/evsel.h"
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#include "util/env.h"
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#include "linux/string.h"
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void arch_evsel__set_sample_weight(struct evsel *evsel)
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{
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evsel__set_sample_bit(evsel, WEIGHT_STRUCT);
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}
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void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr)
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{
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struct perf_env env = { .total_mem = 0, } ;
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if (!perf_env__cpuid(&env))
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return;
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/*
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* On AMD, precise cycles event sampling internally uses IBS pmu.
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* But IBS does not have filtering capabilities and perf by default
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* sets exclude_guest = 1. This makes IBS pmu event init fail and
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* thus perf ends up doing non-precise sampling. Avoid it by clearing
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* exclude_guest.
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*/
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if (env.cpuid && strstarts(env.cpuid, "AuthenticAMD"))
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attr->exclude_guest = 0;
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free(env.cpuid);
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}
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