* Re: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid()
@ 2021-11-18 17:14 ` Mathieu Poirier
0 siblings, 0 replies; 8+ messages in thread
From: Mathieu Poirier @ 2021-11-18 17:14 UTC (permalink / raw)
To: Leo Yan
Cc: Arnaldo Carvalho de Melo, Namhyung Kim, Suzuki K Poulose,
Mike Leach, John Garry, Will Deacon, Ingo Molnar, Mark Rutland,
Alexander Shishkin, Jiri Olsa, linux-arm-kernel, coresight,
linux-perf-users, linux-kernel
Good morning Leo,
On Sat, Nov 13, 2021 at 10:35:40PM +0800, Leo Yan wrote:
> Currently, cs-etm passes the tid value for both tid and pid parameters
> when calling machine__set_current_tid(), this can lead to confusion for
> thread handling. E.g. we arbitrarily pass the same value for pid and
> tid, perf tool will be misled to consider it is a main thread (see
> thread__main_thread()).
>
> On the other hand, Perf tool only can retrieve tid from Arm CoreSight
> context packet, and we have no chance to know pid (it maps to kernel's
> task_struct::tgid) from hardware tracing data. For this reason, this
> patch passes -1 as pid for function machine__set_current_tid().
>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
> tools/perf/util/cs-etm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index f323adb1af85..eed1a5930072 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -1118,7 +1118,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> if (cs_etm__get_cpu(trace_chan_id, &cpu) < 0)
> return err;
>
> - err = machine__set_current_tid(etm->machine, cpu, tid, tid);
> + err = machine__set_current_tid(etm->machine, cpu, -1, tid);
I remember wondering about what to do with the pid parameter when I wrote this
patch...
Do you have a before-and-after snapshot you can add to the changelog? I also
think it will require a "Fixes" tag. In your next revision please CC James
since you guys are working in that area nowadays.
Thanks,
Mathieu
> if (err)
> return err;
>
> --
> 2.25.1
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid()
2021-11-18 17:14 ` Mathieu Poirier
@ 2021-11-19 0:33 ` Leo Yan
-1 siblings, 0 replies; 8+ messages in thread
From: Leo Yan @ 2021-11-19 0:33 UTC (permalink / raw)
To: Mathieu Poirier
Cc: Arnaldo Carvalho de Melo, Namhyung Kim, Suzuki K Poulose,
Mike Leach, John Garry, Will Deacon, Ingo Molnar, Mark Rutland,
Alexander Shishkin, Jiri Olsa, linux-arm-kernel, coresight,
linux-perf-users, linux-kernel
Hi Mathieu,
On Thu, Nov 18, 2021 at 10:14:12AM -0700, Mathieu Poirier wrote:
> Good morning Leo,
>
> On Sat, Nov 13, 2021 at 10:35:40PM +0800, Leo Yan wrote:
> > Currently, cs-etm passes the tid value for both tid and pid parameters
> > when calling machine__set_current_tid(), this can lead to confusion for
> > thread handling. E.g. we arbitrarily pass the same value for pid and
> > tid, perf tool will be misled to consider it is a main thread (see
> > thread__main_thread()).
> >
> > On the other hand, Perf tool only can retrieve tid from Arm CoreSight
> > context packet, and we have no chance to know pid (it maps to kernel's
> > task_struct::tgid) from hardware tracing data. For this reason, this
> > patch passes -1 as pid for function machine__set_current_tid().
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > tools/perf/util/cs-etm.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index f323adb1af85..eed1a5930072 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -1118,7 +1118,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> > if (cs_etm__get_cpu(trace_chan_id, &cpu) < 0)
> > return err;
> >
> > - err = machine__set_current_tid(etm->machine, cpu, tid, tid);
> > + err = machine__set_current_tid(etm->machine, cpu, -1, tid);
>
> I remember wondering about what to do with the pid parameter when I wrote this
> patch...
>
> Do you have a before-and-after snapshot you can add to the changelog?
I tried to capture log but I didn't observe the difference introduced
by this patch, this might because I didn't per-process mode for
multi-threading case. I will try more case for this.
> I also think it will require a "Fixes" tag. In your next revision please CC James
> since you guys are working in that area nowadays.
Will do. And will Cc James and German in next spin.
Thanks for review and suggestion.
Leo
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid()
@ 2021-11-19 0:33 ` Leo Yan
0 siblings, 0 replies; 8+ messages in thread
From: Leo Yan @ 2021-11-19 0:33 UTC (permalink / raw)
To: Mathieu Poirier
Cc: Arnaldo Carvalho de Melo, Namhyung Kim, Suzuki K Poulose,
Mike Leach, John Garry, Will Deacon, Ingo Molnar, Mark Rutland,
Alexander Shishkin, Jiri Olsa, linux-arm-kernel, coresight,
linux-perf-users, linux-kernel
Hi Mathieu,
On Thu, Nov 18, 2021 at 10:14:12AM -0700, Mathieu Poirier wrote:
> Good morning Leo,
>
> On Sat, Nov 13, 2021 at 10:35:40PM +0800, Leo Yan wrote:
> > Currently, cs-etm passes the tid value for both tid and pid parameters
> > when calling machine__set_current_tid(), this can lead to confusion for
> > thread handling. E.g. we arbitrarily pass the same value for pid and
> > tid, perf tool will be misled to consider it is a main thread (see
> > thread__main_thread()).
> >
> > On the other hand, Perf tool only can retrieve tid from Arm CoreSight
> > context packet, and we have no chance to know pid (it maps to kernel's
> > task_struct::tgid) from hardware tracing data. For this reason, this
> > patch passes -1 as pid for function machine__set_current_tid().
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > tools/perf/util/cs-etm.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index f323adb1af85..eed1a5930072 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -1118,7 +1118,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> > if (cs_etm__get_cpu(trace_chan_id, &cpu) < 0)
> > return err;
> >
> > - err = machine__set_current_tid(etm->machine, cpu, tid, tid);
> > + err = machine__set_current_tid(etm->machine, cpu, -1, tid);
>
> I remember wondering about what to do with the pid parameter when I wrote this
> patch...
>
> Do you have a before-and-after snapshot you can add to the changelog?
I tried to capture log but I didn't observe the difference introduced
by this patch, this might because I didn't per-process mode for
multi-threading case. I will try more case for this.
> I also think it will require a "Fixes" tag. In your next revision please CC James
> since you guys are working in that area nowadays.
Will do. And will Cc James and German in next spin.
Thanks for review and suggestion.
Leo
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid()
2021-11-18 17:14 ` Mathieu Poirier
@ 2021-11-23 3:14 ` Leo Yan
-1 siblings, 0 replies; 8+ messages in thread
From: Leo Yan @ 2021-11-23 3:14 UTC (permalink / raw)
To: Mathieu Poirier
Cc: Arnaldo Carvalho de Melo, Namhyung Kim, Suzuki K Poulose,
Mike Leach, John Garry, Will Deacon, Ingo Molnar, Mark Rutland,
Alexander Shishkin, Jiri Olsa, linux-arm-kernel, coresight,
linux-perf-users, linux-kernel
On Thu, Nov 18, 2021 at 10:14:12AM -0700, Mathieu Poirier wrote:
> Good morning Leo,
>
> On Sat, Nov 13, 2021 at 10:35:40PM +0800, Leo Yan wrote:
> > Currently, cs-etm passes the tid value for both tid and pid parameters
> > when calling machine__set_current_tid(), this can lead to confusion for
> > thread handling. E.g. we arbitrarily pass the same value for pid and
> > tid, perf tool will be misled to consider it is a main thread (see
> > thread__main_thread()).
> >
> > On the other hand, Perf tool only can retrieve tid from Arm CoreSight
> > context packet, and we have no chance to know pid (it maps to kernel's
> > task_struct::tgid) from hardware tracing data. For this reason, this
> > patch passes -1 as pid for function machine__set_current_tid().
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > tools/perf/util/cs-etm.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index f323adb1af85..eed1a5930072 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -1118,7 +1118,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> > if (cs_etm__get_cpu(trace_chan_id, &cpu) < 0)
> > return err;
> >
> > - err = machine__set_current_tid(etm->machine, cpu, tid, tid);
> > + err = machine__set_current_tid(etm->machine, cpu, -1, tid);
>
> I remember wondering about what to do with the pid parameter when I wrote this
> patch...
Some updates after I digged into the pid parameter for
machine__set_current_tid().
During the recording phase, the perf tool will capture events
PERF_RECORD_COMM and PERF_RECORD_FORK; these events contain pid/tid
for profiled program. Below is an example for RECORD_FORK/RECORD_COMM
events in perf data file:
0x89f0 [0x40]: event: 7
.
. ... raw event: size 64 bytes
. 0000: 07 00 00 00 00 20 40 00 59 6d 00 00 59 6d 00 00 ..... @.Ym..Ym..
. 0010: 5a 6d 00 00 59 6d 00 00 00 00 00 00 00 00 00 00 Zm..Ym..........
. 0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0 0 0x89f0 [0x40]: PERF_RECORD_FORK(27993:27994):(27993:27993)
0x8a30 [0x38]: event: 3
.
. ... raw event: size 56 bytes
. 0000: 03 00 00 00 00 00 38 00 59 6d 00 00 5a 6d 00 00 ......8.Ym..Zm..
. 0010: 6d 61 69 6e 00 00 00 00 00 00 00 00 00 00 00 00 main............
. 0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0030: 00 00 00 00 00 00 00 00 ........
0 0 0x8a30 [0x38]: PERF_RECORD_COMM: main:27993/27994
In the reporting phase, perf tool will setup threads structure based on
the RECORD_FORK and RECORD_COMM events. This means perf tool will set
the pid/tid for every thread, e.g. in up case, it allocates thread
context for 'main' program, and its one child thread is setup to
thread->pid_ as '27993' and thread->tid as '27994'.
Afterwards, when perf tool decodes CoreSight trace data and handles
context packet, at the end, machine__update_thread_pid() is invoked
for updating thread's pid:
machine__update_thread_pid(struct machine *machine,
struct thread *th, pid_t pid)
{
if (pid == th->pid_ || pid == -1 || th->pid_ != -1)
return;
...
}
Whatever we pass the pid parameter as tid or '-1' from the caller
function machine__set_current_tid(), it doesn't change anything for the
thread context. Since th->pid_ has been initialized and its value is
not '-1', no matter what's the pid value is passed via argument,
machine__update_thread_pid() will directly bail out. This is why
before we pass 'tid' value rather than '-1' for pid, it doesn't cause
any error.
For this reason, this patch doesn't improve anything. After discussed
with Mathieu offline, I decided to drop this change. So update the
info in case someone is interested in the relevant info.
Thanks,
Leo
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH v1] perf cs-etm: Pass -1 as pid value for machine__set_current_tid()
@ 2021-11-23 3:14 ` Leo Yan
0 siblings, 0 replies; 8+ messages in thread
From: Leo Yan @ 2021-11-23 3:14 UTC (permalink / raw)
To: Mathieu Poirier
Cc: Arnaldo Carvalho de Melo, Namhyung Kim, Suzuki K Poulose,
Mike Leach, John Garry, Will Deacon, Ingo Molnar, Mark Rutland,
Alexander Shishkin, Jiri Olsa, linux-arm-kernel, coresight,
linux-perf-users, linux-kernel
On Thu, Nov 18, 2021 at 10:14:12AM -0700, Mathieu Poirier wrote:
> Good morning Leo,
>
> On Sat, Nov 13, 2021 at 10:35:40PM +0800, Leo Yan wrote:
> > Currently, cs-etm passes the tid value for both tid and pid parameters
> > when calling machine__set_current_tid(), this can lead to confusion for
> > thread handling. E.g. we arbitrarily pass the same value for pid and
> > tid, perf tool will be misled to consider it is a main thread (see
> > thread__main_thread()).
> >
> > On the other hand, Perf tool only can retrieve tid from Arm CoreSight
> > context packet, and we have no chance to know pid (it maps to kernel's
> > task_struct::tgid) from hardware tracing data. For this reason, this
> > patch passes -1 as pid for function machine__set_current_tid().
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > tools/perf/util/cs-etm.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > index f323adb1af85..eed1a5930072 100644
> > --- a/tools/perf/util/cs-etm.c
> > +++ b/tools/perf/util/cs-etm.c
> > @@ -1118,7 +1118,7 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
> > if (cs_etm__get_cpu(trace_chan_id, &cpu) < 0)
> > return err;
> >
> > - err = machine__set_current_tid(etm->machine, cpu, tid, tid);
> > + err = machine__set_current_tid(etm->machine, cpu, -1, tid);
>
> I remember wondering about what to do with the pid parameter when I wrote this
> patch...
Some updates after I digged into the pid parameter for
machine__set_current_tid().
During the recording phase, the perf tool will capture events
PERF_RECORD_COMM and PERF_RECORD_FORK; these events contain pid/tid
for profiled program. Below is an example for RECORD_FORK/RECORD_COMM
events in perf data file:
0x89f0 [0x40]: event: 7
.
. ... raw event: size 64 bytes
. 0000: 07 00 00 00 00 20 40 00 59 6d 00 00 59 6d 00 00 ..... @.Ym..Ym..
. 0010: 5a 6d 00 00 59 6d 00 00 00 00 00 00 00 00 00 00 Zm..Ym..........
. 0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0 0 0x89f0 [0x40]: PERF_RECORD_FORK(27993:27994):(27993:27993)
0x8a30 [0x38]: event: 3
.
. ... raw event: size 56 bytes
. 0000: 03 00 00 00 00 00 38 00 59 6d 00 00 5a 6d 00 00 ......8.Ym..Zm..
. 0010: 6d 61 69 6e 00 00 00 00 00 00 00 00 00 00 00 00 main............
. 0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0030: 00 00 00 00 00 00 00 00 ........
0 0 0x8a30 [0x38]: PERF_RECORD_COMM: main:27993/27994
In the reporting phase, perf tool will setup threads structure based on
the RECORD_FORK and RECORD_COMM events. This means perf tool will set
the pid/tid for every thread, e.g. in up case, it allocates thread
context for 'main' program, and its one child thread is setup to
thread->pid_ as '27993' and thread->tid as '27994'.
Afterwards, when perf tool decodes CoreSight trace data and handles
context packet, at the end, machine__update_thread_pid() is invoked
for updating thread's pid:
machine__update_thread_pid(struct machine *machine,
struct thread *th, pid_t pid)
{
if (pid == th->pid_ || pid == -1 || th->pid_ != -1)
return;
...
}
Whatever we pass the pid parameter as tid or '-1' from the caller
function machine__set_current_tid(), it doesn't change anything for the
thread context. Since th->pid_ has been initialized and its value is
not '-1', no matter what's the pid value is passed via argument,
machine__update_thread_pid() will directly bail out. This is why
before we pass 'tid' value rather than '-1' for pid, it doesn't cause
any error.
For this reason, this patch doesn't improve anything. After discussed
with Mathieu offline, I decided to drop this change. So update the
info in case someone is interested in the relevant info.
Thanks,
Leo
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 8+ messages in thread