lkml.org 
[lkml]   [2022]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v5 1/8] perf record ibs: Warn about sampling period skew
Hi Ravi,

On Tue, May 31, 2022 at 8:27 PM Ravi Bangoria <ravi.bangoria@amd.com> wrote:
>
> Samples without an L3 miss are discarded and counter is reset with
> random value (between 1-15 for fetch pmu and 1-127 for op pmu) when
> IBS L3 miss filtering is enabled. This causes a sampling period skew
> but there is no way to reconstruct aggregated sampling period. So
> print a warning at perf record if user sets l3missonly=1.
>
> Ex:
> # perf record -c 10000 -C 0 -e ibs_op/l3missonly=1/
> WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled
> and tagged operation does not cause L3 Miss. This causes sampling period skew.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
> Acked-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/arch/x86/util/evsel.c | 49 ++++++++++++++++++++++++++++++++
> tools/perf/util/evsel.c | 7 +++++
> tools/perf/util/evsel.h | 1 +
> 3 files changed, 57 insertions(+)
>
> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
> index 88306183d629..fceb904902ab 100644
> --- a/tools/perf/arch/x86/util/evsel.c
> +++ b/tools/perf/arch/x86/util/evsel.c
> @@ -5,6 +5,7 @@
> #include "util/env.h"
> #include "util/pmu.h"
> #include "linux/string.h"
> +#include "util/debug.h"
>
> void arch_evsel__set_sample_weight(struct evsel *evsel)
> {
> @@ -60,3 +61,51 @@ bool arch_evsel__must_be_in_group(const struct evsel *evsel)
> (!strcasecmp(evsel->name, "slots") ||
> strcasestr(evsel->name, "topdown"));
> }
> +
> +static void ibs_l3miss_warn(void)
> +{
> + pr_warning(
> +"WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled\n"
> +"and tagged operation does not cause L3 Miss. This causes sampling period skew.\n");
> +}
> +
> +void arch__post_evsel_config(struct evsel *evsel, struct perf_event_attr *attr)
> +{
> + struct perf_pmu *evsel_pmu, *ibs_fetch_pmu, *ibs_op_pmu;
> + static int warned_once;
> + /* 0: Uninitialized, 1: Yes, -1: No */
> + static int is_amd;
> +
> + if (warned_once || is_amd == -1)
> + return;
> +
> + if (!is_amd) {
> + struct perf_env *env = evsel__env(evsel);
> +
> + if (!perf_env__cpuid(env) || !env->cpuid ||
> + !strstarts(env->cpuid, "AuthenticAMD")) {
> + is_amd = -1;
> + return;
> + }
> + is_amd = 1;
> + }
> +
> + evsel_pmu = evsel__find_pmu(evsel);
> + if (!evsel_pmu)
> + return;
> +
> + ibs_fetch_pmu = perf_pmu__find("ibs_fetch");
> + ibs_op_pmu = perf_pmu__find("ibs_op");
> +
> + if (ibs_fetch_pmu && ibs_fetch_pmu->type == evsel_pmu->type) {
> + if (attr->config & (1ULL << 59)) {

It'd be nice if we used a macro or something instead of the
magic number.

> + ibs_l3miss_warn();
> + warned_once = 1;
> + }
> + } else if (ibs_op_pmu && ibs_op_pmu->type == evsel_pmu->type) {
> + if (attr->config & (1ULL << 16)) {

Ditto.

Thanks,
Namhyung


> + ibs_l3miss_warn();
> + warned_once = 1;
> + }
> + }
> +}
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index ce499c5da8d7..8fea51a9cd90 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1091,6 +1091,11 @@ void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_un
> {
> }
>
> +void __weak arch__post_evsel_config(struct evsel *evsel __maybe_unused,
> + struct perf_event_attr *attr __maybe_unused)
> +{
> +}
> +
> static void evsel__set_default_freq_period(struct record_opts *opts,
> struct perf_event_attr *attr)
> {
> @@ -1366,6 +1371,8 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
> */
> if (evsel__is_dummy_event(evsel))
> evsel__reset_sample_bit(evsel, BRANCH_STACK);
> +
> + arch__post_evsel_config(evsel, attr);
> }
>
> int evsel__set_filter(struct evsel *evsel, const char *filter)
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 73ea48e94079..92bed8e2f7d8 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -297,6 +297,7 @@ 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);
> +void arch__post_evsel_config(struct evsel *evsel, 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);
> --
> 2.31.1
>

\
 
 \ /
  Last update: 2022-06-02 22:31    [W:0.127 / U:1.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site