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Message-ID: <Zw1vcnX-HdnmJMU1@google.com>
Date: Mon, 14 Oct 2024 12:22:26 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org,
Ravi Bangoria <ravi.bangoria@....com>,
Mark Rutland <mark.rutland@....com>,
James Clark <james.clark@....com>, Kajol Jain <kjain@...ux.ibm.com>,
Thomas Richter <tmricht@...ux.ibm.com>,
Atish Patra <atishp@...shpatra.org>,
Palmer Dabbelt <palmer@...osinc.com>,
Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH 7/8] perf tools: Check fallback error and order
Hi Ian,
On Thu, Oct 03, 2024 at 03:38:01PM -0700, Namhyung Kim wrote:
> On Thu, Oct 03, 2024 at 10:32:47AM -0700, Ian Rogers wrote:
> > On Thu, Oct 3, 2024 at 10:06 AM Namhyung Kim <namhyung@...nel.org> wrote:
> > >
> > > On Tue, Oct 01, 2024 at 03:21:50PM -0700, Ian Rogers wrote:
> > > > On Tue, Oct 1, 2024 at 2:36 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > > > >
> > > > > On Tue, Oct 01, 2024 at 11:00:20AM -0700, Ian Rogers wrote:
> > > > > > On Mon, Sep 30, 2024 at 5:20 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > > > > > >
> > > > > > > The perf_event_open might fail due to various reasons, so blindly
> > > > > > > reducing precise_ip level might not be the best way to deal with it.
> > > > > > >
> > > > > > > It seems the kernel return -EOPNOTSUPP when PMU doesn't support the
> > > > > > > given precise level. Let's try again with the correct error code.
> > > > > > >
> > > > > > > This caused a problem on AMD, as it stops on precise_ip of 2 for IBS but
> > > > > > > user events with exclude_kernel=1 cannot make progress. Let's add the
> > > > > > > evsel__handle_error_quirks() to this case specially. I plan to work on
> > > > > > > the kernel side to improve this situation but it'd still need some
> > > > > > > special handling for IBS.
> > > > > > >
> > > > > > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > > > > > > ---
> > > > > > > tools/perf/util/evsel.c | 27 +++++++++++++++++++++------
> > > > > > > 1 file changed, 21 insertions(+), 6 deletions(-)
> > > > > > >
> > > > > > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > > > > > index 32e30c293d0c6198..ef8356260eea54cd 100644
> > > > > > > --- a/tools/perf/util/evsel.c
> > > > > > > +++ b/tools/perf/util/evsel.c
> > > > > > > @@ -2419,6 +2419,20 @@ static bool evsel__detect_missing_features(struct evsel *evsel)
> > > > > > > return false;
> > > > > > > }
> > > > > > >
> > > > > > > +static bool evsel__handle_error_quirks(struct evsel *evsel, int error)
> > > > > > > +{
> > > > > > > + /* AMD IBS doesn't support exclude_kernel, forward it to core PMU */
> > > > > >
> > > > > > Should the quirk handling be specific to evsels with the IBS PMU given
> > > > > > the comment above? ie this is a PMU specific workaround rather than an
> > > > > > AMD specific workaround, however, the PMU only exists on AMD :-)
> > > > > >
> > > > > > > + if (error == -EINVAL && evsel->precise_max && evsel->core.attr.precise_ip &&
> > > > > > > + evsel->core.attr.exclude_kernel && x86__is_amd_cpu()) {
> > > > > >
> > > > > > So here rather than x86__is_amd_cpu it would be
> > > > > > !strcmp(evsel->pmu->name, "ibs_...") . But it may be cleaner to move
> > > > > > the logic into pmu.c.
> > > > >
> > > > > I guess the problem is that AMD driver does implicit forwarding to IBS
> > > > > if the legacy hardware events have precise_ip. So it might have just
> > > > > core pmu (or no pmu) in the evsel.
> > > >
> > > > I think the no PMU case should probably have a PMU possibly similar to
> > > > the tool PMU in:
> > > > https://lore.kernel.org/all/20240912190341.919229-1-irogers@google.com/
> > > > But that's not in place yet. You can always use
> > > > perf_pmus__scan_core(NULL) or
> > > > perf_pmus__find_by_type(evsel->core.attr.type or PERF_TYPE_RAW).
> > > > evsel->pmu->is_core && x86__is_amd_cpu() would identify an AMD core
> > > > PMU whereas the code above could fire for IBS or other PMUs.
> > >
> > > But IBS is the only PMU on AMD that provides precise_ip IIRC. So I
> > > don't think other events would have it nor have any effect on changing
> > > the value. So maybe we can skip the PMU scanning and just drop to 0?
> >
> > cpu supports precise_ip as it forwards it to IBS, IBS is an ambiguous
> > term as there are ibs_op and ibs_fetch PMUs. The code is using values
> > in the attribute to infer the PMU that is being used, it feels it
> > would be more intention revealing to do things like:
> > ```
> > if (error == ... && perf_pmu__is_ibs_op_or_fetch(evsel->pmu)) ..
> > ```
>
> I guess it'd get a core PMU for the default cycles event. I think the
> intention is already confusing with the implicit forwarding.
What about this?
---8<---
>From 70d39fb5c2956ba264a292f112f7fd7272dc91be Mon Sep 17 00:00:00 2001
From: Namhyung Kim <namhyung@...nel.org>
Date: Tue, 3 Sep 2024 22:50:09 -0700
Subject: [PATCH] perf tools: Check fallback error and order
The perf_event_open might fail due to various reasons, so blindly
reducing precise_ip level might not be the best way to deal with it.
It seems the kernel return -EOPNOTSUPP when PMU doesn't support the
given precise level. Let's try again with the correct error code.
This caused a problem on AMD, as it stops on precise_ip of 2 for IBS but
user events with exclude_kernel=1 cannot make progress. Let's add the
evsel__handle_error_quirks() to this case specially. I plan to work on
the kernel side to improve this situation but it'd still need some
special handling for IBS.
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
tools/perf/util/evsel.c | 50 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 44 insertions(+), 6 deletions(-)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 476658143822c346..2c45c55222c43dd4 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2246,6 +2246,43 @@ static bool evsel__detect_missing_features(struct evsel *evsel)
return false;
}
+/*
+ * AMD core PMU forwards some events with precise_ip to IBS implicitly.
+ * This logic matches to the kernel function (core_pmu_ibs_config).
+ */
+static bool evsel__is_implicit_ibs_event(struct evsel *evsel)
+{
+ if (evsel->core.attr.precise_ip == 0 || !x86__is_amd_cpu())
+ return false;
+
+ if (evsel->core.attr.type == PERF_TYPE_HARDWARE &&
+ evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES)
+ return true;
+
+ if (evsel->core.attr.type == PERF_TYPE_RAW &&
+ (evsel->core.attr.config == 0x76 || evsel->core.attr.config == 0xc1))
+ return true;
+
+ return false;
+}
+
+static bool evsel__handle_error_quirks(struct evsel *evsel, int error)
+{
+ /*
+ * AMD IBS doesn't support exclude_kernel, forward it back to the core
+ * PMU by clearing precise_ip only if it's from precise_max (:P).
+ */
+ if (error == -EINVAL && evsel__is_implicit_ibs_event(evsel) &&
+ evsel->core.attr.exclude_kernel && evsel->precise_max) {
+ evsel->core.attr.precise_ip = 0;
+ pr_debug2_peo("removing precise_ip on AMD\n");
+ display_attr(&evsel->core.attr);
+ return true;
+ }
+
+ return false;
+}
+
static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
struct perf_thread_map *threads,
int start_cpu_map_idx, int end_cpu_map_idx)
@@ -2366,9 +2403,6 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
return 0;
try_fallback:
- if (evsel__precise_ip_fallback(evsel))
- goto retry_open;
-
if (evsel__ignore_missing_thread(evsel, perf_cpu_map__nr(cpus),
idx, threads, thread, err)) {
/* We just removed 1 thread, so lower the upper nthreads limit. */
@@ -2385,11 +2419,15 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
if (err == -EMFILE && rlimit__increase_nofile(&set_rlimit))
goto retry_open;
- if (err != -EINVAL || idx > 0 || thread > 0)
- goto out_close;
+ if (err == -EOPNOTSUPP && evsel__precise_ip_fallback(evsel))
+ goto retry_open;
- if (evsel__detect_missing_features(evsel))
+ if (err == -EINVAL && evsel__detect_missing_features(evsel))
goto fallback_missing_features;
+
+ if (evsel__handle_error_quirks(evsel, err))
+ goto retry_open;
+
out_close:
if (err)
threads->err_thread = thread;
--
2.47.0.rc1.288.g06298d1525-goog
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