linux-kernel - RE: [PATCH V3 1/5] perf/x86/intel/uncore: customized pmu event read for client IMC uncore

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F077537DCA32@SHSMSX103.ccr.corp.intel.com>
Date:   Thu, 2 Nov 2017 14:06:10 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: RE: [PATCH V3 1/5] perf/x86/intel/uncore: customized pmu event read
 for client IMC uncore

> On Thu, 2 Nov 2017, Thomas Gleixner wrote:
> > On Thu, 2 Nov 2017, Liang, Kan wrote:
> > > > On Tue, 24 Oct 2017, kan.liang@...el.com wrote:
> > > > > -	if (event->hw.idx >= UNCORE_PMC_IDX_FIXED)
> > > > > +	if (event->hw.idx == UNCORE_PMC_IDX_FIXED)
> > > > >  		shift = 64 - uncore_fixed_ctr_bits(box);
> > > > >  	else
> > > > >  		shift = 64 - uncore_perf_ctr_bits(box); diff --git
> > > > > a/arch/x86/events/intel/uncore_snb.c
> > > > > b/arch/x86/events/intel/uncore_snb.c
> > > > > index db1127c..9d5cd3f 100644
> > > > > --- a/arch/x86/events/intel/uncore_snb.c
> > > > > +++ b/arch/x86/events/intel/uncore_snb.c
> > > > > @@ -498,6 +498,30 @@ static void snb_uncore_imc_event_del(struct
> > > > perf_event *event, int flags)
> > > > >  	snb_uncore_imc_event_stop(event, PERF_EF_UPDATE);  }
> > > > >
> > > > > +static void snb_uncore_imc_event_read(struct perf_event *event) {
> > > > > +	struct intel_uncore_box *box = uncore_event_to_box(event);
> > > > > +	u64 prev_count, new_count, delta;
> > > > > +	int shift;
> > > > > +
> > > > > +	if (event->hw.idx >= UNCORE_PMC_IDX_FIXED)
> > > >
> > > > And this needs to be >= because?
> > >
> > > Patch 5/5 will clean up the client IMC uncore.
> > > Before that, we still need it to make client IMC uncore work.
> > >
> > > This patch isolates the >= case for client IMC uncore.
> >
> > Fair enough. A comment to that effect (even when removed later) would
> > have avoided that question.
> 
> Thinking more about it. The current code only supports the fixed one, right?
> So why would it deal with anything > FIXED?
> 

There are two free running counters in IMC.
To support the second one, the previous code implicitly do
UNCORE_PMC_IDX_FIXED + 1.
So it has to deal with > FIXED case.

	case SNB_UNCORE_PCI_IMC_DATA_READS:
		base = SNB_UNCORE_PCI_IMC_DATA_READS_BASE;
		idx = UNCORE_PMC_IDX_FIXED;
		break;
	case SNB_UNCORE_PCI_IMC_DATA_WRITES:
		base = SNB_UNCORE_PCI_IMC_DATA_WRITES_BASE;
		idx = UNCORE_PMC_IDX_FIXED + 1;
		break;
	default:
		return -EINVAL;

Thanks,
Kan