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 09:55:11 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "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>,
        "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 9:53 AM, Liang, Kan <kan.liang@...el.com> wrote:
>> 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.
>
You can measure the bandwidth and utilization on the GP. I am doing it all
the time.

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