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: <ZiK6G3aM+K92lq0w@lizhi-Precision-Tower-5810>
Date: Fri, 19 Apr 2024 14:38:19 -0400
From: Frank Li <Frank.li@....com>
To: Will Deacon <will@...nel.org>
Cc: Xu Yang <xu.yang_2@....com>, 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

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");

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

Frank

> 
> Will