linux-kernel - Re: [PATCH 1/2] Documentation: perf: Update documentation for ThunderX2 PMU uncore driver

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Date:   Fri, 28 Jun 2019 09:45:00 +0530
From:   Ganapatrao Kulkarni <gklkml16@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     Ganapatrao Kulkarni <gkulkarni@...vell.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Will.Deacon@....com" <Will.Deacon@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "corbet@....net" <corbet@....net>, jnair@...vell.com,
        jglauber@...vell.com, rrichter@...vell.com
Subject: Re: [PATCH 1/2] Documentation: perf: Update documentation for
 ThunderX2 PMU uncore driver

Hi Will,

On Thu, Jun 27, 2019 at 9:52 PM Will Deacon <will@...nel.org> wrote:
>
> On Thu, Jun 27, 2019 at 11:01:18AM +0100, Will Deacon wrote:
> > On Fri, Jun 14, 2019 at 05:42:45PM +0000, Ganapatrao Kulkarni wrote:
> > > From: Ganapatrao Kulkarni <ganapatrao.kulkarni@...vell.com>
> > >
> > > Add documentation for Cavium Coherent Processor Interconnect (CCPI2) PMU.
> > >
> > > Signed-off-by: Ganapatrao Kulkarni <gkulkarni@...vell.com>
> > > ---
> > >  Documentation/perf/thunderx2-pmu.txt | 20 +++++++++++---------
> > >  1 file changed, 11 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/Documentation/perf/thunderx2-pmu.txt b/Documentation/perf/thunderx2-pmu.txt
> > > index dffc57143736..62243230abc3 100644
> > > --- a/Documentation/perf/thunderx2-pmu.txt
> > > +++ b/Documentation/perf/thunderx2-pmu.txt
> > > @@ -2,24 +2,26 @@ Cavium ThunderX2 SoC Performance Monitoring Unit (PMU UNCORE)
> > >  =============================================================
> > >
> > >  The ThunderX2 SoC PMU consists of independent, system-wide, per-socket
> > > -PMUs such as the Level 3 Cache (L3C) and DDR4 Memory Controller (DMC).
> > > +PMUs such as the Level 3 Cache (L3C), DDR4 Memory Controller (DMC) and
> > > +Cavium Coherent Processor Interconnect (CCPI2).
> > >
> > >  The DMC has 8 interleaved channels and the L3C has 16 interleaved tiles.
> > >  Events are counted for the default channel (i.e. channel 0) and prorated
> > >  to the total number of channels/tiles.
> > >
> > > -The DMC and L3C support up to 4 counters. Counters are independently
> > > -programmable and can be started and stopped individually. Each counter
> > > -can be set to a different event. Counters are 32-bit and do not support
> > > -an overflow interrupt; they are read every 2 seconds.
> > > +The DMC, L3C support up to 4 counters and CCPI2 support up to 8 counters.
> >
> > The DMC and L3C support up to 4 counters, while the CCPI2 supports up to 8
> > counters.
> >
> > > +Counters are independently programmable and can be started and stopped
> > > +individually. Each counter can be set to a different event. DMC and L3C
> > > +Counters are 32-bit and do not support an overflow interrupt; they are read
> >
> > Counters -> counters
> >
> > > +every 2 seconds. CCPI2 counters are 64-bit.
> >
> > Assuming CCPI2 also doesn't support an overflow interrupt, I'd reword these
> > two sentences as:
> >
> >   None of the counters support an overflow interrupt and therefore sampling
> >   events are unsupported. The DMC and L3C counters are 32-bit and read every
> >   2 seconds. The CCPI2 counters are 64-bit and assumed not to overflow in
> >   normal operation.
>

Thanks for the comments, will update in v2.
Yes, CCPI2 is 64bit counter and there is no overflow issue.

> Mark reminded me that these are system PMUs and therefore sampling is
> unsupported irrespective of the presence of an overflow interrupt, so you
> can drop that part from the text.

sure.
>
> Sorry for the confusion,
>
> Will

Thanks,
Ganapat