linux-kernel - RE: [PATCH V5 4/8] perf/x86/intel/uncore: add new data structures for free running counters

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Date:   Fri, 19 Jan 2018 17:53:16 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "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 V5 4/8] perf/x86/intel/uncore: add new data structures
 for free running counters

> On Fri, Jan 19, 2018 at 03:15:00PM +0000, Liang, Kan wrote:
> > >
> > > On Thu, Jan 18, 2018 at 05:43:10PM +0000, Liang, Kan wrote:
> > > > In the uncore document, there is no event-code assigned to free
> > > > running
> > > counters.
> > > > Some events need to be defined to indicate the free running counters.
> > > > The events are encoded as event-code + umask-code.
> > > >
> > > > The event-code for all free running counters is 0xff, which is the
> > > > same as the fixed counters.
> > >
> > > Is it possible to count the same things using the generic counters?
> > >
> >
> > Yes, there are events for generic counters to count bandwidth and
> > utilization.
> >
> > The reasons of introducing free running counters are
> > - To provide highly valuable information (bandwidth and utilization)
> >    which most of the customers are interested in
> > - To save on the precious generic counters
> 
> _IF_ the exact same counters are available on the GPs then we must use the
> same event code for them and use event scheduling to place them on
> fixed/free-running counters when possible.

OK. I will check if there are the exact same events on GPs for
those free running counters.

Thanks,
Kan

> 
> That's what we do for the CPU PMU's fixed counters too.
> 
> Don't invent magic event codes just because.