Re: [PATCH v2 1/9] perf: Add EVENT_ATTR_ID to simplify event attributes

[liuqi (BA)]

Hi Will,

Thanks for reviewing this patch.

On 2021/6/1 21:10, Will Deacon wrote:
> On Wed, May 19, 2021 at 05:51:51PM +0800, Qi Liu wrote:
> > Similar EVENT_ATTR macros are defined in many PMU drivers,
> > like HiSilicon PMU driver, Arm PMU driver, Arm SMMU PMU
> > driver. So Add a generic macro to simplify code.
> >
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> > Signed-off-by: Qi Liu <liuqi115@xxxxxxxxxx>
> > ---
> >   include/linux/perf_event.h | 6 ++++++
> >   kernel/events/core.c       | 2 ++
> >   2 files changed, 8 insertions(+)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index f5a6a2f..d0aa74e 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -1576,6 +1576,12 @@ static struct perf_pmu_events_attr _var = {				    \
> >   	.event_str	= _str,						    \
> >   };
> >   
> > +#define PMU_EVENT_ATTR_ID(_name, _id)					     \
> > +	(&((struct perf_pmu_events_attr[]) {				     \
> > +		{ .attr = __ATTR(_name, 0444, perf_event_sysfs_show, NULL),  \
> > +		  .id = _id, }						     \
> > +	})[0].attr.attr)
> > +
> >   #define PMU_FORMAT_ATTR(_name, _format)					\
> >   static ssize_t								\
> >   _name##_show(struct device *dev,					\
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 0ac818b..330d9cc 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -13295,6 +13295,8 @@ ssize_t perf_event_sysfs_show(struct device *dev, struct device_attribute *attr,
> >   
> >   	if (pmu_attr->event_str)
> >   		return sprintf(page, "%s\n", pmu_attr->event_str);
> > +	else
> > +		return sprintf(page, "config=%#llx\n", pmu_attr->id);
>
> I think it's a really bad idea to hardcode this here. For example, I think
> this patch series breaks user ABI for the SMMU PMU which used to print:
>
> 	"event=0x%02llx\n"
>
> and by the looks of it many of the other conversions are unsound too.
Got it, so I'll use pmu_attr->event_str here, for example,
SMMU_EVENT_ATTR(cycles, "event=0x00")

As PMU_EVENT_ATTR_STRING is already defined in linux/perf_event.h，and is 
used in drivers of multi architectures, add a new common macro might be 
better than modify PMU_EVENT_ATTR_STRING.
Do you have any suggestion about the name of new common macro?

Thanks,
Qi
> I'm all for a common macro, but the string needs to be determined by the
> driver.
>
> Will
> .