RE: [RFC PATCH v10 0/8] TPEBS counting mode support

From: Wang, Weilin
Date: Fri May 31 2024 - 03:01:03 EST

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> -----Original Message-----
> From: Namhyung Kim <namhyung@xxxxxxxxxx>
> Sent: Thursday, May 30, 2024 11:37 PM
> To: Wang, Weilin <weilin.wang@xxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>; Arnaldo Carvalho de Melo
> <acme@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Ingo Molnar
> <mingo@xxxxxxxxxx>; Alexander Shishkin
> <alexander.shishkin@xxxxxxxxxxxxxxx>; Jiri Olsa <jolsa@xxxxxxxxxx>; Hunter,
> Adrian <adrian.hunter@xxxxxxxxx>; Kan Liang <kan.liang@xxxxxxxxxxxxxxx>;
> linux-perf-users@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Taylor, Perry
> <perry.taylor@xxxxxxxxx>; Alt, Samantha <samantha.alt@xxxxxxxxx>; Biggers,
> Caleb <caleb.biggers@xxxxxxxxx>
> Subject: Re: [RFC PATCH v10 0/8] TPEBS counting mode support
>
> Hello,
>
> On Tue, May 28, 2024 at 11:43 PM <weilin.wang@xxxxxxxxx> wrote:
> >
> > From: Weilin Wang <weilin.wang@xxxxxxxxx>
> >
> > I have tried not to count retire_latency events but did not succeed.
> > In particular, I tried the following methods:
> > - Convert retire_latency event to dummy event in event parser.
> > - Early bail out in evsel__open_cpu() and store_evsel_ids().
> >
> > The first method fails and causes non-retire_latency events with the same
> event
> > name return 0 count.
> >
> > The second method fails and causes all the events in the same group
> returning
> > "<not counted>" results.
>
> Can you please describe where it fails? Is it failing on other events
> because the tpebs event is a leader of the group? I think you wanted
> to avoid having it in the leader position. If we can skip any actual
> operations (open/close/enable/disable/read) for the tpebs events, then
> it could be fine..

It does not fail with the code in this patch set. But if I make it return directly
from tpebs_start() in evsel__open_cpu(), it will cause segfault. The segfault is
caused by store_evsel_id(). I could add another early return from store_evsel_id()
if the evsel->retire_lat is true.

After this change, it will eventually run and give me <not counted> results
like below:

<not counted> event1
<not counted> event2
xx event1:R

In a different case, it may seem to work (xxxxxx stands for some valid value):

xxxxxxx event1
xxxxxxx event2
xxxxxxx event3
xx event1:R

In the first case, the event1, event2 and event1:R are scheduled in the same
group. On the other hand, in the second case, event1, event2 and event3 are
in one group, while event1:R is in a different group.

Based on these two different type of results, I believe the failure happens in
the group that include a :R event. I've added the change to arch_evlist__cmp()
so that a :R event would not be a leader of the group.

I think I've made evsel__open_cpu() return before it create fd and make
store_evsel_id() not to read and store fd. I'm not sure where I'm missing. Please
let me know if you have any suggestions.

Thanks,
Weilin

>
> Thanks,
> Namhyung
>
> >
> > Because of above, the retire_latency event will still run in counting mode.
> >
> > Other changes in v10:
> > - Change perf record fork from perf stat to evsel. All the major operations
> > like tpebs start, stop, read_evsel should directly work through evsel.
> > - Make intel-tpebs x86_64 only. This change is cross-compiled to arm64.
> > - Put tpebs code to intel-tepbs and simplify intel-tpebs APIs to minimum
> number
> > of functions and variables. Update funtion name and variable names to use
> > consistent prefix. Also improve error handling.
> > - Integrate code patch from Ian for the :R parser.
> > - Update MTL metrics to TMA 4.8.
> >
> > V9: https://lore.kernel.org/all/20240521173952.3397644-1-
> weilin.wang@xxxxxxxxx/
> >
> > Changes in v9:
> > - Update the retire_latency result print and metric calculation method.
> Plugin
> > the value to evsel so that no special code is required.
> > - Update --control:fifo to use pipe instead of named pipe.
> > - Add test for TPEBS counting mode.
> > - Update Document with more details.
> >
> > Changes in v8:
> > - In this revision, the code is updated to base on Ian's patch on R modifier
> > parser https://lore.kernel.org/lkml/20240428053616.1125891-3-
> irogers@xxxxxxxxxx/
> > After this change, there is no special code required for R modifier in
> > metricgroup.c and metricgroup.h files.
> >
> > Caveat of this change:
> > Ideally, we will need to add special handling to skip counting events with R
> > modifier in evsel. Currently, this is not implemented so the event with :R will
> > be both counted and sampled. Usually, in a metric formula that uses
> retire_latency,
> > it would already require to count the event. As a result, we will endup count
> the
> > same event twice. This should be able to be handled properly when we
> finalize our
> > design on evsel R modifier support.
> >
> > - Move TPEBS specific code out from main perf stat code to separate files in
> > util/intel-tpebs.c and util/intel-tpebs.h. [Namhyung]
> > - Use --control:fifo to ack perf stat from forked perf record instead of
> sleep(2) [Namhyung]
> > - Add introductions about TPEBS and R modifier in Documents. [Namhyung]
> >
> >
> > Changes in v7:
> > - Update code and comments for better code quality [Namhyung]
> > - Add a separate commit for perf data [Namhyung]
> > - Update retire latency print function to improve alignment [Namhyung]
> >
> > Changes in v6:
> > - Update code and add comments for better code quality [Namhyung]
> > - Remove the added fd var and directly pass the opened fd to data.file.fd
> [Namhyung]
> > - Add kill() to stop perf record when perf stat exists early [Namhyung]
> > - Add command opt check to ensure only start perf record when -a/-C given
> [Namhyung]
> > - Squash commits [Namhyung]
> >
> > Changes in v5:
> > - Update code and add comments for better code quality [Ian]
> >
> > Changes in v4:
> > - Remove uncessary debug print and update code and comments for better
> > readability and quality [Namhyung]
> > - Update mtl metric json file with consistent TmaL1 and TopdownL1
> metricgroup
> >
> > Changes in v3:
> > - Remove ':' when event name has '@' [Ian]
> > - Use 'R' as the modifier instead of "retire_latency" [Ian]
> >
> > Changes in v2:
> > - Add MTL metric file
> > - Add more descriptions and example to the patch [Arnaldo]
> >
> > Here is an example of running perf stat to collect a metric that uses
> > retire_latency value of event MEM_INST_RETIRED.STLB_HIT_STORES on a
> MTL system.
> >
> > In this simple example, there is no MEM_INST_RETIRED.STLB_HIT_STORES
> sample.
> > Therefore, the MEM_INST_RETIRED.STLB_HIT_STORES:p count and
> retire_latency value
> > are all 0.
> >
> > ./perf stat -M tma_dtlb_store -a -- sleep 1
> >
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.000 MB - ]
> >
> > Performance counter stats for 'system wide':
> >
> > 181,047,168 cpu_core/TOPDOWN.SLOTS/ # 0.6 %
> tma_dtlb_store
> > 3,195,608 cpu_core/topdown-retiring/
> > 40,156,649 cpu_core/topdown-mem-bound/
> > 3,550,925 cpu_core/topdown-bad-spec/
> > 117,571,818 cpu_core/topdown-fe-bound/
> > 57,118,087 cpu_core/topdown-be-bound/
> > 69,179 cpu_core/EXE_ACTIVITY.BOUND_ON_STORES/
> > 4,582 cpu_core/MEM_INST_RETIRED.STLB_HIT_STORES/
> > 30,183,104 cpu_core/CPU_CLK_UNHALTED.DISTRIBUTED/
> > 30,556,790 cpu_core/CPU_CLK_UNHALTED.THREAD/
> > 168,486 cpu_core/DTLB_STORE_MISSES.WALK_ACTIVE/
> > 0.00 MEM_INST_RETIRED.STLB_HIT_STORES:p 0 0
> >
> > 1.003105924 seconds time elapsed
> >
> > v1:
> > TPEBS is one of the features provided by the next generation of Intel PMU.
> > Please refer to Section 8.4.1 of "Intel® Architecture Instruction Set
> Extensions
> > Programming Reference" [1] for more details about this feature.
> >
> > This set of patches supports TPEBS in counting mode. The code works in the
> > following way: it forks a perf record process from perf stat when
> retire_latency
> > of one or more events are used in a metric formula. Perf stat would send a
> > SIGTERM signal to perf record before it needs the retire latency value for
> > metric calculation. Perf stat will then process sample data to extract the
> > retire latency data for metric calculations. Currently, the code uses the
> > arithmetic average of retire latency values.
> >
> > [1] https://www.intel.com/content/www/us/en/content-
> details/812218/intel-architecture-instruction-set-extensions-programming-
> reference.html?wapkw=future%20features
> >
> >
> > Ian Rogers (1):
> > perf parse-events: Add a retirement latency modifier
> >
> > Weilin Wang (7):
> > perf data: Allow to use given fd in data->file.fd
> > perf stat: Fork and launch perf record when perf stat needs to get
> > retire latency value for a metric.
> > perf stat: Plugin retire_lat value from sampled data to evsel
> > perf vendor events intel: Add MTL metric json files
> > perf stat: Add command line option for enabling tpebs recording
> > perf Document: Add TPEBS to Documents
> > perf test: Add test for Intel TPEBS counting mode
> >
> > tools/perf/Documentation/perf-list.txt | 1 +
> > tools/perf/Documentation/topdown.txt | 30 +
> > tools/perf/arch/x86/util/evlist.c | 6 +
> > tools/perf/builtin-stat.c | 8 +
> > .../arch/x86/meteorlake/metricgroups.json | 140 +
> > .../arch/x86/meteorlake/mtl-metrics.json | 2595 +++++++++++++++++
> > .../perf/tests/shell/test_stat_intel_tpebs.sh | 19 +
> > tools/perf/util/Build | 1 +
> > tools/perf/util/data.c | 7 +-
> > tools/perf/util/evsel.c | 26 +
> > tools/perf/util/evsel.h | 6 +
> > tools/perf/util/intel-tpebs.c | 397 +++
> > tools/perf/util/intel-tpebs.h | 48 +
> > tools/perf/util/parse-events.c | 2 +
> > tools/perf/util/parse-events.h | 1 +
> > tools/perf/util/parse-events.l | 3 +-
> > 16 files changed, 3288 insertions(+), 2 deletions(-)
> > create mode 100644 tools/perf/pmu-
> events/arch/x86/meteorlake/metricgroups.json
> > create mode 100644 tools/perf/pmu-events/arch/x86/meteorlake/mtl-
> metrics.json
> > create mode 100755 tools/perf/tests/shell/test_stat_intel_tpebs.sh
> > create mode 100644 tools/perf/util/intel-tpebs.c
> > create mode 100644 tools/perf/util/intel-tpebs.h
> >
> > --
> > 2.43.0
> >

Next message: Gautam Menghani: "Re: [PATCH] arch/powerpc/kvm: Fix doorbell emulation by adding DPDES support"
Previous message: Claudiu: "[PATCH v9 9/9] dt-bindings: watchdog: renesas,wdt: Document RZ/G3S support"
In reply to: Namhyung Kim: "Re: [RFC PATCH v10 0/8] TPEBS counting mode support"
Next in thread: Namhyung Kim: "Re: [RFC PATCH v10 0/8] TPEBS counting mode support"
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