[PATCH] tools/perf: Fix aggr_printout to display cpu field irrespective of core value
Ian Rogers
irogers at google.com
Sun Oct 2 10:47:08 AEDT 2022
On Thu, Sep 29, 2022 at 5:56 AM James Clark <james.clark at arm.com> wrote:
>
>
>
> On 29/09/2022 09:49, Athira Rajeev wrote:
> >
> >
> >> On 28-Sep-2022, at 9:05 PM, James Clark <james.clark at arm.com> wrote:
> >>
> >>
> >>
> >
> > Hi James,
> >
> > Thanks for looking at the patch and sharing review comments.
> >
> >> On 13/09/2022 12:57, Athira Rajeev wrote:
> >>> perf stat includes option to specify aggr_mode to display
> >>> per-socket, per-core, per-die, per-node counter details.
> >>> Also there is option -A ( AGGR_NONE, -no-aggr ), where the
> >>> counter values are displayed for each cpu along with "CPU"
> >>> value in one field of the output.
> >>>
> >>> Each of the aggregate mode uses the information fetched
> >>> from "/sys/devices/system/cpu/cpuX/topology" like core_id,
> >>
> >> I thought that this wouldn't apply to the cpu field because cpu is
> >> basically interchangeable as an index in cpumap, rather than anything
> >> being read from the topology file.
> >
> > The cpu value is filled in this function:
> >
> > Function : aggr_cpu_id__cpu
> > Code: util/cpumap.c
> >
> >>
> >>> physical_package_id. Utility functions in "cpumap.c" fetches
> >>> this information and populates the socket id, core id, cpu etc.
> >>> If the platform does not expose the topology information,
> >>> these values will be set to -1. Example, in case of powerpc,
> >>> details like physical_package_id is restricted to be exposed
> >>> in pSeries platform. So id.socket, id.core, id.cpu all will
> >>> be set as -1.
> >>>
> >>> In case of displaying socket or die value, there is no check
> >>> done in the "aggr_printout" function to see if it points to
> >>> valid socket id or die. But for displaying "cpu" value, there
> >>> is a check for "if (id.core > -1)". In case of powerpc pSeries
> >>> where detail like physical_package_id is restricted to be
> >>> exposed, id.core will be set to -1. Hence the column or field
> >>> itself for CPU won't be displayed in the output.
> >>>
> >>> Result for per-socket:
> >>>
> >>> <<>>
> >>> perf stat -e branches --per-socket -a true
> >>>
> >>> Performance counter stats for 'system wide':
> >>>
> >>> S-1 32 416,851 branches
> >>> <<>>
> >>>
> >>> Here S has -1 in above result. But with -A option which also
> >>> expects CPU in one column in the result, below is observed.
> >>>
> >>> <<>>
> >>> /bin/perf stat -e instructions -A -a true
> >>>
> >>> Performance counter stats for 'system wide':
> >>>
> >>> 47,146 instructions
> >>> 45,226 instructions
> >>> 43,354 instructions
> >>> 45,184 instructions
> >>> <<>>
> >>>
> >>> If the cpu id value is pointing to -1 also, it makes sense
> >>> to display the column in the output to replicate the behaviour
> >>> or to be in precedence with other aggr options(like per-socket,
> >>> per-core). Remove the check "id.core" so that CPU field gets
> >>> displayed in the output.
> >>
> >> Why would you want to print -1 out? Seems like the if statement was a
> >> good one to me, otherwise the output looks a bit broken to users. Are
> >> the other aggregation modes even working if -1 is set for socket and
> >> die? Maybe we need to not print -1 in those cases or exit earlier with a
> >> failure.
> >>
> >> The -1 value has a specific internal meaning which is "to not
> >> aggregate". It doesn't mean "not set".
> >
> > Currently, this check is done only for printing cpu value.
> > For socket/die/core values, this check is not done. Pasting an
> > example snippet from a powerpc system ( specifically from pseries platform where
> > the value is set to -1 )
> >
> > ./perf stat --per-core -a -C 1 true
> >
> > Performance counter stats for 'system wide':
> >
> > S-1-D-1-C-1 1 1.06 msec cpu-clock # 1.018 CPUs utilized
> > S-1-D-1-C-1 1 2 context-switches # 1.879 K/sec
> > S-1-D-1-C-1 1 0 cpu-migrations # 0.000 /sec
> >
> > Here though the value is -1, we are displaying it. Where as in case of cpu, the first column will be
> > empty since we do a check before printing.
> >
> > Example:
> >
> > ./perf stat --per-core -A -C 1 true
> >
> > Performance counter stats for 'CPU(s) 1':
> >
> > 0.88 msec cpu-clock # 1.022 CPUs utilized
> > 2 context-switches
> > 0 cpu-migrations
> >
> >
> > No sure, whether there are scripts out there, which consume the current format and
> > not displaying -1 may break it. That is why we tried with change to remove check for cpu, similar to
> > other modes like socket, die, core etc.
>
> I wouldn't worry about that because there are json and CSV modes which
> are machine readable, and -1 is already not always displayed. If
> anything this change here is also likely to break parsing by adding -1
> where it wasn't before.
>
> >
> > Also perf code ie “aggr_cpu_id__empty” in util/cpumap.c initialises the
> > values to -1 . I was checking to see where we are mapping -1 to “to not aggregate”.
> > What I could find is AGGR_NONE ( which is for no-aggr ) has value as zero.
> >
> > Reference: defined in util/stat.h
> >
> > enum aggr_mode {
> > AGGR_NONE,
> >
>
> That enum is never written to any of the cpumap members, that defines
> the mode of how to fill the cpu map instead. 0 is a valid value, for
> example "CPU 0". -1 is used as a special case and shouldn't be displayed
> IMO.
>
> Did you see my comment in the code below about the bad merge? Could that
> not be related to your issue?
I'm suspicious of this too. In Claire's patch:
case AGGR_NONE:
- if (evsel->percore && !config->percore_show_thread) {
- fprintf(config->output, "S%d-D%d-C%*d%s",
- id.socket,
- id.die,
- config->csv_output ? 0 : -3,
- id.core, config->csv_sep);
- } else if (id.cpu.cpu > -1) {
- fprintf(config->output, "CPU%*d%s",
- config->csv_output ? 0 : -7,
- id.cpu.cpu, config->csv_sep);
+ if (config->json_output) {
+ if (evsel->percore && !config->percore_show_thread) {
+ fprintf(config->output, "\"core\" :
\"S%d-D%d-C%d\"",
+ id.socket,
+ id.die,
+ id.core);
+ } else if (id.core > -1) {
+ fprintf(config->output, "\"cpu\" : \"%d\", ",
+ id.cpu.cpu);
+ }
+ } else {
+ if (evsel->percore && !config->percore_show_thread) {
+ fprintf(config->output, "S%d-D%d-C%*d%s",
+ id.socket,
+ id.die,
+ config->csv_output ? 0 : -3,
+ id.core, config->csv_sep);
+ } else if (id.core > -1) {
+ fprintf(config->output, "CPU%*d%s",
+ config->csv_output ? 0 : -7,
+ id.cpu.cpu, config->csv_sep);
+ }
}
break;
The old code was using "id.cpu.cpu > -1" while the new code is
"id.core > -1". The value printed is id.cpu.cpu and so testing id.core
makes less sense to me. Going back to the original patch:
https://lore.kernel.org/lkml/20210811224317.1811618-1-cjense@google.com/
case AGGR_NONE:
- if (evsel->percore && !config->percore_show_thread) {
- fprintf(config->output, "S%d-D%d-C%*d%s",
- id.socket,
- id.die,
- config->csv_output ? 0 : -3,
- id.core, config->csv_sep);
+ if (config->json_output) {
+ if (evsel->percore && !config->percore_show_thread) {
+ fprintf(config->output, "\"core\" : \"S%d-D%d-C%d\"",
+ id.socket,
+ id.die,
+ id.core);
+ } else if (id.core > -1) {
+ fprintf(config->output, "\"cpu\" : \"%d\", ",
+ evsel__cpus(evsel)->map[id.core]);
+ }
+ } else {
+ if (evsel->percore && !config->percore_show_thread) {
+ fprintf(config->output, "S%d-D%d-C%*d%s",
+ id.socket,
+ id.die,
+ config->csv_output ? 0 : -3,
+ id.core, config->csv_sep);
} else if (id.core > -1) {
fprintf(config->output, "CPU%*d%s",
config->csv_output ? 0 : -7,
evsel__cpus(evsel)->map[id.core],
config->csv_sep);
- }
+ }
+ }
+
break;
So testing the id.core isn't a bad index makes sense. However, we
changed from core to CPU here:
https://lore.kernel.org/all/20220105061351.120843-26-irogers@google.com/
and that was because of:
https://lore.kernel.org/r/20220105061351.120843-25-irogers@google.com
So I think the code needs to test CPU and not core. Whether that is
addressing the Power test failures is another matter, as James said we
may need a fix in the tests for that.
Thanks,
Ian
> Or the one about fixing it in the test instead? Or failing early if the
> topology can't be read?
>
> I'm still not convinced that any of the modes where -1 is printed are
> even working properly so it might be best to fix that rather than just
> the printout.
>
> > James, can you point me to reference for that meaning if I have missed anything.
>
> It's here:
>
> /** Identify where counts are aggregated, -1 implies not to aggregate. */
> struct aggr_cpu_id {
>
> >
> > Thanks
> > Athira
> >
> >>
> >>>
> >>> After the fix:
> >>>
> >>> <<>>
> >>> perf stat -e instructions -A -a true
> >>>
> >>> Performance counter stats for 'system wide':
> >>>
> >>> CPU-1 64,034 instructions
> >>> CPU-1 68,941 instructions
> >>> CPU-1 59,418 instructions
> >>> CPU-1 70,478 instructions
> >>> CPU-1 65,201 instructions
> >>> CPU-1 63,704 instructions
> >>> <<>>
> >>>
> >>> This is caught while running "perf test" for
> >>> "stat+json_output.sh" and "stat+csv_output.sh".
> >>
> >> Is it possible to fix the issue by making the tests cope with the lack
> >> of the CPU id?
> >>
> >>>
> >>> Reported-by: Disha Goel <disgoel at linux.vnet.ibm.com>
> >>> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
> >>> ---
> >>> tools/perf/util/stat-display.c | 6 ++----
> >>> 1 file changed, 2 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> >>> index b82844cb0ce7..1b751a730271 100644
> >>> --- a/tools/perf/util/stat-display.c
> >>> +++ b/tools/perf/util/stat-display.c
> >>> @@ -168,10 +168,9 @@ static void aggr_printout(struct perf_stat_config *config,
> >>> id.socket,
> >>> id.die,
> >>> id.core);
> >>> - } else if (id.core > -1) {
> >>> + } else
> >>
> >> This should have been "id.cpu.cpu > -1". Looks like it was changed by
> >> some kind of bad merge or rebase in df936cadfb because there is no
> >> obvious justification for the change to .core in that commit.
> >
> >>
> >>> fprintf(config->output, "\"cpu\" : \"%d\", ",
> >>> id.cpu.cpu);
> >>> - }
> >>> } else {
> >>> if (evsel->percore && !config->percore_show_thread) {
> >>> fprintf(config->output, "S%d-D%d-C%*d%s",
> >>> @@ -179,11 +178,10 @@ static void aggr_printout(struct perf_stat_config *config,
> >>> id.die,
> >>> config->csv_output ? 0 : -3,
> >>> id.core, config->csv_sep);
> >>> - } else if (id.core > -1) {
> >>> + } else
> >>> fprintf(config->output, "CPU%*d%s",
> >>> config->csv_output ? 0 : -7,
> >>> id.cpu.cpu, config->csv_sep);
> >>> - }
> >>> }
> >>> break;
> >>> case AGGR_THREAD:
> >
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