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

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Message-ID: <CAKTKpr48Cmcs8u81EZeMMndP1XwaNOMCE-r00vhE6ysK3CUsrw@mail.gmail.com>
Date:   Thu, 22 Aug 2019 09:30:56 +0530
From:   Ganapatrao Kulkarni <gklkml16@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        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>,
        "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 Wed, Aug 21, 2019 at 10:23 PM Will Deacon <will@...nel.org> wrote:
>
> On Tue, Aug 13, 2019 at 12:03:45PM +0100, Mark Rutland wrote:
> > On Tue, Aug 13, 2019 at 04:25:15PM +0530, Ganapatrao Kulkarni wrote:
> > > 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.
>
> tbf, my complaint was actually about some macros applying to the whole
> PMU whilst others refer only to DMC/L3C and this not being apparent from
> the naming:
>
> https://lkml.org/lkml/2019/6/27/250
>
> so I'm fine having TX2_PMU_DMC_L3C_MAX_COUNTERS and
> TX2_PMU_CCPI2_MAX_COUNTERS, but that sort of naming needs to be consistent
> unless the macro/definition really applies to both. That fed the suggestion
> that GET_EVENTID could be generic and switch on the event type internally
> instead of at the caller.

Thanks Will for the clarification.
I will send new version with changes as suggested.

>
> Will

Thanks,
Ganapat