linux-kernel - Re: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes

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Message-ID: <CALcN6mi0j=A_j59p5UNJ7tvMR0u5AH_ryYKCn8Af8P0iySMLOQ@mail.gmail.com>
Date:   Mon, 6 Feb 2017 13:46:07 -0800
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     Shivappa Vikas <vikas.shivappa@...el.com>
Cc:     "Luck, Tony" <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "Anvin, H Peter" <h.peter.anvin@...el.com>
Subject: Re: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes

On Mon, Feb 6, 2017 at 1:36 PM, Shivappa Vikas <vikas.shivappa@...el.com> wrote:
>
>
> On Mon, 6 Feb 2017, Luck, Tony wrote:
>
>>> 12) Whatever fs or syscall is provided instead of perf syscalls, it
>>> should provide total_time_enabled in the way perf does, otherwise is
>>> hard to interpret MBM values.
>>
>>
>> It seems that it is hard to define what we even mean by memory bandwidth.
>>
>> If you are measuring just one task and you find that the total number of
>> bytes
>> read is 1GB at some point, and one second later the total bytes is 2GB,
>> then
>> it is clear that the average bandwidth for this process is 1GB/s. If you
>> know
>> that the task was only running for 50% of the cycles during that 1s
>> interval,
>> you could say that it is doing 2GB/s ... which is I believe what you were
>> thinking when you wrote #12 above.  But whether that is right depends a
>> bit on *why* it only ran 50% of the time. If it was time-sliced out by the
>> scheduler ... then it may have been trying to be a 2GB/s app. But if it
>> was waiting for packets from the network, then it really is using 1 GB/s.
>
>
> Is the requirement is to have both enabled and run time or just enabled time
> (enabled time must be easy to report - just the wall time from start trace
> to end trace)?

Both, but since the original requirements dropped rotation, then
total_running == total_enabled.

>
> This is not reported correctly in the upstream perf cqm and for
> cgroup -C we dont report it either (since we report the package).

using the -x option shows the run time and the % enabled. Many tools
uses that csv output.

>
> Thanks,
> Vikas
>
>
>>
>> All bets are off if you are measuring a service that consists of several
>> tasks running concurrently. All you can really talk about is the aggregate
>> average bandwidth (total bytes / wall-clock time). It makes no sense to
>> try and factor in how much cpu time each of the individual tasks got.
>>
>> -Tony
>>
>