Re: [RESEND PATCH 09/12] perf: Extend perf_output_read

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jun 20, 2024 at 11:00:28AM +0200, Peter Zijlstra wrote:
> On Tue, Jun 18, 2024 at 08:10:41AM -0700, kan.liang@linux.intel.com wrote:
> > From: Kan Liang <kan.liang@linux.intel.com>
> > 
> > The event may have been updated in the PMU-specific implementation,
> > e.g., Intel PEBS counters snapshotting. The common code should not
> > read and overwrite the value.
> > 
> > The PERF_SAMPLE_READ in the data->sample_type can be used to detect
> > whether the PMU-specific value is available. If yes, avoid the
> > pmu->read() in the common code.
> > 
> > Reviewed-by: Andi Kleen <ak@linux.intel.com>
> > Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> > ---
> >  kernel/events/core.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> > 
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 8f908f077935..733e507948e6 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -7243,7 +7243,7 @@ static void perf_output_read_one(struct perf_output_handle *handle,
> >  
> >  static void perf_output_read_group(struct perf_output_handle *handle,
> >  			    struct perf_event *event,
> > -			    u64 enabled, u64 running)
> > +			    u64 enabled, u64 running, bool read)
> >  {
> >  	struct perf_event *leader = event->group_leader, *sub;
> >  	u64 read_format = event->attr.read_format;
> > @@ -7265,7 +7265,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> >  	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
> >  		values[n++] = running;
> >  
> > -	if ((leader != event) &&
> > +	if ((leader != event) && read &&
> >  	    (leader->state == PERF_EVENT_STATE_ACTIVE))
> >  		leader->pmu->read(leader);
> >  
> > @@ -7280,7 +7280,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> >  	for_each_sibling_event(sub, leader) {
> >  		n = 0;
> >  
> > -		if ((sub != event) &&
> > +		if ((sub != event) && read &&
> >  		    (sub->state == PERF_EVENT_STATE_ACTIVE))
> >  			sub->pmu->read(sub);
> >  
> > @@ -7307,7 +7307,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> >   * on another CPU, from interrupt/NMI context.
> >   */
> >  static void perf_output_read(struct perf_output_handle *handle,
> > -			     struct perf_event *event)
> > +			     struct perf_event *event,
> > +			     bool read)
> >  {
> >  	u64 enabled = 0, running = 0, now;
> >  	u64 read_format = event->attr.read_format;
> > @@ -7325,7 +7326,7 @@ static void perf_output_read(struct perf_output_handle *handle,
> >  		calc_timer_values(event, &now, &enabled, &running);
> >  
> >  	if (event->attr.read_format & PERF_FORMAT_GROUP)
> > -		perf_output_read_group(handle, event, enabled, running);
> > +		perf_output_read_group(handle, event, enabled, running, read);
> >  	else
> >  		perf_output_read_one(handle, event, enabled, running);
> >  }
> > @@ -7367,7 +7368,7 @@ void perf_output_sample(struct perf_output_handle *handle,
> >  		perf_output_put(handle, data->period);
> >  
> >  	if (sample_type & PERF_SAMPLE_READ)
> > -		perf_output_read(handle, event);
> > +		perf_output_read(handle, event, !(data->sample_flags & PERF_SAMPLE_READ));
> >  
> >  	if (sample_type & PERF_SAMPLE_CALLCHAIN) {
> >  		int size = 1;
> 
> this can't be right. The output is order sensitive. If a
> PERF_SAMPLE_READ is part of the PERF_RECORD_SAMPLE, it must be in this
> location.

Oh, n/n. I read that wrong. I'll try again after a break.