linux-kernel - Re: [PATCH v3 2/2] drivers/perf: Add CCPI2 PMU support in ThunderX2 UNCORE driver.

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Message-ID: <20190813110345.GD866@lakrids.cambridge.arm.com>
Date:   Tue, 13 Aug 2019 12:03:45 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Ganapatrao Kulkarni <gklkml16@...il.com>
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@...nel.org" <will@...nel.org>,
        "corbet@....net" <corbet@....net>,
        Jayachandran Chandrasekharan Nair <jnair@...vell.com>,
        Robert Richter <rrichter@...vell.com>,
        Jan Glauber <jglauber@...vell.com>
Subject: Re: [PATCH v3 2/2] drivers/perf: Add CCPI2 PMU support in ThunderX2
 UNCORE driver.

On Tue, Aug 13, 2019 at 04:25:15PM +0530, Ganapatrao Kulkarni wrote:
> Hi Mark,
> 
> On Mon, Aug 12, 2019 at 5:31 PM Mark Rutland <mark.rutland@....com> wrote:
> >
> > On Tue, Jul 23, 2019 at 09:16:28AM +0000, Ganapatrao Kulkarni wrote:
> > > CCPI2 is a low-latency high-bandwidth serial interface for connecting
> > > ThunderX2 processors. This patch adds support to capture CCPI2 perf events.
> >
> > It would be worth pointing out in the commit message how the CCPI2
> > counters differ from the others. I realise you have that in the body of
> > patch 1, but it's critical information when reviewing this patch...
> 
> Ok, I will add in next version.
> >
> > >
> > > Signed-off-by: Ganapatrao Kulkarni <gkulkarni@...vell.com>
> > > ---
> > >  drivers/perf/thunderx2_pmu.c | 248 ++++++++++++++++++++++++++++++-----
> > >  1 file changed, 214 insertions(+), 34 deletions(-)
> > >
> > > diff --git a/drivers/perf/thunderx2_pmu.c b/drivers/perf/thunderx2_pmu.c
> > > index 43d76c85da56..a4e1273eafa3 100644
> > > --- a/drivers/perf/thunderx2_pmu.c
> > > +++ b/drivers/perf/thunderx2_pmu.c
> > > @@ -17,22 +17,31 @@
> > >   */
> > >
> > >  #define TX2_PMU_MAX_COUNTERS         4
> >
> > Shouldn't this be 8 now?
> 
> It is kept unchanged to 4(as suggested by Will), which is same for
> both L3 and DMC.
> For CCPI2 this macro is not used.

Hmmm....

I disagree with that suggestion given that this also affects the
active_counters bitmap size (and thus it is not correctly sized as of
this patch), and it doesn't really save us much.

I think it would be better to bump this to 8 and always update the
events array, even though it will be unused for CCPI2. That's less
surprising, needs fewer special-cases, and we can use the hrtimer
function pointer alone to determine if we need to do any hrtimer work.

Thanks,
Mark.