linux-kernel - Re: [PATCH v10 3/8] perf: imx_perf: let the driver manage the counter usage rather the user

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Message-ID: <20240423114539.4jseauipidvwo7bh@hippo>
Date: Tue, 23 Apr 2024 19:45:39 +0800
From: Xu Yang <xu.yang_2@....com>
To: Frank Li <Frank.li@....com>
Cc: Will Deacon <will@...nel.org>, mark.rutland@....com, robh+dt@...nel.org,
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
	shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
	festevam@...il.com, john.g.garry@...cle.com, jolsa@...nel.org,
	namhyung@...nel.org, irogers@...gle.com, mike.leach@...aro.org,
	peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
	alexander.shishkin@...ux.intel.com, adrian.hunter@...el.com,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	imx@...ts.linux.dev
Subject: Re: [PATCH v10 3/8] perf: imx_perf: let the driver manage the
 counter usage rather the user

Hi Frank,

On Fri, Apr 19, 2024 at 02:38:19PM -0400, Frank Li wrote:
> On Fri, Apr 19, 2024 at 04:49:13PM +0100, Will Deacon wrote:
> > On Mon, Apr 15, 2024 at 02:13:15PM +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.
> > > 
> > > 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 attr will be kept for back-compatible but all the
> > > value passed down by counter=<n> will be ignored. 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
> > > Changes in v9:
> > >  - keep 'counter' attr for back-compatible
> > > Changes in v10:
> > >  - add some explanation about 'counter' attr in commit message
> > > ---
> > >  drivers/perf/fsl_imx9_ddr_perf.c | 168 ++++++++++++++++++-------------
> > >  1 file changed, 100 insertions(+), 68 deletions(-)
> > 
> > [...]
> > 
> > > @@ -245,8 +249,8 @@ 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");
> > > +PMU_FORMAT_ATTR(counter, "config:16-23");
> > 
> > Although these mappings are advertised in sysfs, I don't think we can
> > change them because userspace could be relying on them. I also can't
> > find any examples of other PMU drivers in the kernel changing these
> > mappings after being merged, so please keep tthem the same.
> > 
> > If you need to expand the properties to be 16-bit, then you'll need to
> > split them into 2x8-bit fields.
> 
> I just see tools/perf/tests/pmu.c: { "krava01", "config:0-1,62-63\n", }
> So I supposed "config:" supported below format
> 
> PMU_FORMAT_ATTR(event, "config:0-7,16-19");

It works.

Thanks,
Xu Yang

> 
> I just want to confim with you because I have not found other perf driver
> using such format yet.
> 
> Frank
> 
> > 
> > Will