linux-kernel - Re: [PATCH RFC 4/7] perf pmu: Rename uncore symbols to include system PMUs

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Date:   Wed, 12 Feb 2020 13:08:15 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org, will@...nel.org, ak@...ux.intel.com,
        linuxarm@...wei.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        james.clark@....com, zhangshaokun@...ilicon.com,
        robin.murphy@....com
Subject: Re: [PATCH RFC 4/7] perf pmu: Rename uncore symbols to include
 system PMUs

On Tue, Feb 11, 2020 at 03:36:39PM +0000, John Garry wrote:
> On 11/02/2020 14:43, Jiri Olsa wrote:
> > > root@(none)$ pwd
> > > /sys/bus/event_source/devices/smmuv3_pmcg_100020
> > > root@(none)$ ls -l
> > > total 0
> > > -r--r--r--    1 root     root          4096 Feb 10 14:50 cpumask
> > > drwxr-xr-x    2 root     root             0 Feb 10 14:50 events
> > > drwxr-xr-x    2 root     root             0 Feb 10 14:50 format
> > > -rw-r--r--    1 root     root          4096 Feb 10 14:50
> > > perf_event_mux_interval_ms
> > > drwxr-xr-x    2 root     root             0 Feb 10 14:50 power
> > > lrwxrwxrwx    1 root     root             0 Feb 10 14:50 subsystem ->
> > > ../../bus/event_source
> > > -r--r--r--    1 root     root          4096 Feb 10 14:50 type
> > > -rw-r--r--    1 root     root          4096 Feb 10 14:50 uevent
> > > 
> > > 
> > > Other PMU drivers which I have checked in drivers/perf also have the same.
> > > 
> > > Indeed I see no way to differentiate whether a PMU is an uncore or system.
> > > So that is why I change the name to cover both. Maybe there is a better name
> > > than the verbose pmu_is_uncore_or_sys().
> > > 
> > > > I don't see the connection here with the sysid or '_sys' checking,
> > > > that's just telling which ID to use when looking for an alias, no?
> > > So the connection is that in perf_pmu__find_map(), for a given PMU, the
> > > matching is now extended from only core or uncore PMUs to also these system
> > > PMUs. And I use the sysid to find an aliasing table for any system PMUs
> > > present.
> 
> Hi Jirka,
> 
> > I see.. can't we just check sysid for uncore PMUs?
> 
> x86 will still alias PMUs (uncore or CPU) based on an alias table matched to
> the cpuid, as it is today. x86 has the benefit of fixed uncore PMUs for a
> given cpuid.

ok, I did mean 'on addition' to the cpuid checks

> 
> For other archs whose uncore or system PMUs are not fixed for a given CPU -
> like arm - we will support matching uncore and system PMUs on cpuid or
> sysid.
> 
> Uncore PMUs are a grey area for arm, as they may or may not be tied to a
> specific cpuid, so we will need to support both matching methods.
> 
> because
> > that's what the code is doing, right?
> 
> Not exactly.
> 
> The code will match on an alias table matched to the cpuid and also an alias
> table matched to the sysid (if perf could actually get a sysid and there is
> a table matching that sysid).
> 
> I hope that this makes sense....

right,  please make sure this kind of explanation is in changelog
or better in the code comment 

thanks,
jirka