Re: [PATCH] perf topdown: Correct leader selection with sample_read enabled

Liang, Kan
2024-06-27T15:12:27Z

Hi Dapeng,

On 2024-06-14 5:39 p.m., Dapeng Mi wrote:
> Addresses an issue where, in the absence of a topdown metrics event
> within a sampling group, the slots event was incorrectly bypassed as
> the sampling leader when sample_read was enabled.
>
> perf record -e '{slots,branches}:S' -c 10000 -vv sleep 1
>
> In this case, the slots event should be sampled as leader but the
> branches event is sampled in fact like the verbose output shows.
>
> perf_event_attr:
> type 4 (cpu)
> size 168
> config 0x400 (slots)
> sample_type IP|TID|TIME|READ|CPU|IDENTIFIER
> read_format ID|GROUP|LOST
> disabled 1
> sample_id_all 1
> exclude_guest 1
> ------------------------------------------------------------
> sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 5
> ------------------------------------------------------------
> perf_event_attr:
> type 0 (PERF_TYPE_HARDWARE)
> size 168
> config 0x4 (PERF_COUNT_HW_BRANCH_INSTRUCTIONS)
> { sample_period, sample_freq } 10000
> sample_type IP|TID|TIME|READ|CPU|IDENTIFIER
> read_format ID|GROUP|LOST
> sample_id_all 1
> exclude_guest 1
>
> The sample period of slots event instead of branches event is reset to
> 0.
>
> This fix ensures the slots event remains the leader under these
> conditions.

This should be just one of the issues with the slots/topdown related
sampling read.

If adding one more topdown event, the sampling read may still be broken.
perf record -e "{slots,instructions,topdown-retiring}:S" -C0 sleep 1
WARNING: events were regrouped to match PMUs
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument)
for event (topdown-retiring).

That may require Yanfei's patch.
https://lore.kernel.org/lkml/20240411144852.2507143-1-yanfei.xu@intel.com/

Please give it try and summarize all the required patches for the
topdown sampling read feature.

Besides, we need a test for the sampling read as well.
Ian has provided a very good base. Please add a topdown sampling read
case on top of it as well.
https://lore.kernel.org/lkml/CAP-5=fUkg-cAXTb+3wbFOQCfdXgpQeZw40XHjfrNFbnBD=NMXg@mail.gmail.com/

Thanks,
Kan

>
> Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> ---
> tools/perf/arch/x86/util/topdown.c | 42 ++++++++++++++++++++++++++++--
> 1 file changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/arch/x86/util/topdown.c b/tools/perf/arch/x86/util/topdown.c
> index 3f9a267d4501..aea6896bbb57 100644
> --- a/tools/perf/arch/x86/util/topdown.c
> +++ b/tools/perf/arch/x86/util/topdown.c
> @@ -1,6 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
> #include "api/fs/fs.h"
> #include "util/evsel.h"
> +#include "util/evlist.h"
> #include "util/pmu.h"
> #include "util/pmus.h"
> #include "util/topdown.h"
> @@ -31,6 +32,32 @@ bool topdown_sys_has_perf_metrics(void)
> return has_perf_metrics;
> }
>
> +static int perf_pmus__topdown_event(void *vstate, struct pmu_event_info *info)
> +{
> + if (!strcmp(info->name, (char *)vstate))
> + return 1;
> +
> + return 0;
> +}
> +
> +static bool is_topdown_metric_event(struct evsel *event)
> +{
> + struct perf_pmu *pmu;
> +
> + if (!topdown_sys_has_perf_metrics())
> + return false;
> +
> + if (event->core.attr.type != PERF_TYPE_RAW)
> + return false;
> +
> + pmu = perf_pmus__find_by_type(PERF_TYPE_RAW);
> + if (pmu && perf_pmu__for_each_event(pmu, false, event->name,
> + perf_pmus__topdown_event))
> + return true;
> +
> + return false;
> +}
> +
> #define TOPDOWN_SLOTS 0x0400
>
> /*
> @@ -41,11 +68,22 @@ bool topdown_sys_has_perf_metrics(void)
> */
> bool arch_topdown_sample_read(struct evsel *leader)
> {
> + struct evsel *event;
> +
> if (!evsel__sys_has_perf_metrics(leader))
> return false;
>
> - if (leader->core.attr.config == TOPDOWN_SLOTS)
> - return true;
> + if (leader->core.attr.config != TOPDOWN_SLOTS)
> + return false;
> +
> + /*
> + * If slots event as leader event but no topdown metric events in group,
> + * slots event should still sample as leader.
> + */
> + evlist__for_each_entry(leader->evlist, event) {
> + if (event != leader && is_topdown_metric_event(event))
> + return true;
> + }
>
> return false;
> }
>
> base-commit: 92e5605a199efbaee59fb19e15d6cc2103a04ec2