linux-kernel - RE: [EXT] Re: [PATCH v8 3/8] perf: imx_perf: let the driver manage the counter usage rather the user

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Message-ID:
 <DU2PR04MB882209413AB62531713166B38C062@DU2PR04MB8822.eurprd04.prod.outlook.com>
Date: Wed, 10 Apr 2024 07:39:46 +0000
From: Xu Yang <xu.yang_2@....com>
To: Will Deacon <will@...nel.org>
CC: Frank Li <frank.li@....com>, "mark.rutland@....com"
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Subject: RE: [EXT] Re: [PATCH v8 3/8] perf: imx_perf: let the driver manage
 the counter usage rather the user

Hi Will,

> 
> On Fri, Mar 22, 2024 at 02:39:25PM +0800, Xu Yang wrote:
> > In current design, the user of perf app needs to input counter ID to count
> > events. However, this is not user-friendly since the user needs to lookup
> > the map table to find the counter. Instead of letting the user to input
> > the counter, let this driver to manage the counters in this patch.
> 
> I think we still have to support the old interface so that we don't break
> those existing users (even if the driver just ignores whatever counter ID
> is provided in a backwards-compatible way).
> 
> > This will be implemented by:
> >  1. allocate counter 0 for cycle event.
> >  2. find unused counter from 1-10 for reference events.
> >  3. allocate specific counter for counter-specific events.
> >
> > In this patch, counter attribute is removed too. To mark counter-specific
> > events, counter ID will be encoded into perf_pmu_events_attr.id.
> >
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > Signed-off-by: Xu Yang <xu.yang_2@....com>
> >
> > ---
> > Changes in v6:
> >  - new patch
> > Changes in v7:
> >  - no changes
> > Changes in v8:
> >  - add Rb tag
> > ---
> >  drivers/perf/fsl_imx9_ddr_perf.c | 168 ++++++++++++++++++-------------
> >  1 file changed, 99 insertions(+), 69 deletions(-)
> >
> > diff --git a/drivers/perf/fsl_imx9_ddr_perf.c b/drivers/perf/fsl_imx9_ddr_perf.c
> > index 0017f2c9ef91..b728719b494c 100644
> > --- a/drivers/perf/fsl_imx9_ddr_perf.c
> > +++ b/drivers/perf/fsl_imx9_ddr_perf.c
> > @@ -245,14 +249,12 @@ static const struct attribute_group ddr_perf_events_attr_group = {
> >       .attrs = ddr_perf_events_attrs,
> >  };
> >
> > -PMU_FORMAT_ATTR(event, "config:0-7");
> > -PMU_FORMAT_ATTR(counter, "config:8-15");
> > +PMU_FORMAT_ATTR(event, "config:0-15");
> 
> Sadly, this is a user-visible change so I think it will break old tools,
> won't it?

For imx ddr pmu, most of the people will use metrics rather event itself,
and we have speficy the format of event parameters in metrics table.
The parameters is also updated in this patchset.

And to easy use for user, the counter should be hidden (transparent) to
user after I had talk with Frank. Then, the user need't to look up the event
table to find which counter to use. 

So this patchset will basically not break the usage of perf tools and will
improve practicality.

Thanks,
Xu Yang


> 
> Will