linux-kernel - Re: [PATCH 01/14] x86/cqm: Intel Resource Monitoring Documentation

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Date:   Fri, 23 Dec 2016 13:32:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Cc:     vikas.shivappa@...el.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, tglx@...utronix.de, ravi.v.shankar@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, andi.kleen@...el.com,
        davidcc@...gle.com, eranian@...gle.com, hpa@...or.com
Subject: Re: [PATCH 01/14] x86/cqm: Intel Resource Monitoring Documentation

On Fri, Dec 16, 2016 at 03:12:55PM -0800, Vikas Shivappa wrote:
> +Continuous monitoring
> +---------------------
> +A new file cont_monitoring is added to perf_cgroup which helps to enable
> +cqm continuous monitoring. Enabling this field would start monitoring of
> +the cgroup without perf being launched. This can be used for long term
> +light weight monitoring of tasks/cgroups.
> +
> +To enable continuous monitoring of cgroup p1.
> +#echo 1 > /sys/fs/cgroup/perf_event/p1/perf_event.cqm_cont_monitoring
> +
> +To disable continuous monitoring of cgroup p1.
> +#echo 0 > /sys/fs/cgroup/perf_event/p1/perf_event.cqm_cont_monitoring
> +
> +To read the counters at the end of monitoring perf can be used.
> +
> +LAZY and NOLAZY Monitoring
> +--------------------------
> +LAZY:
> +By default when monitoring is enabled, the RMIDs are not allocated
> +immediately and allocated lazily only at the first sched_in.
> +There are 2-4 RMIDs per logical processor on each package. So if a dual
> +package has 48 logical processors, there would be upto 192 RMIDs on each
> +package = total of 192x2 RMIDs.
> +There is a possibility that RMIDs can runout and in that case the read
> +reports an error since there was no RMID available to monitor for an
> +event.
> +
> +NOLAZY:
> +When user wants guaranteed monitoring, he can enable the 'monitoring
> +mask' which is basically used to specify the packages he wants to
> +monitor. The RMIDs are statically allocated at open and failure is
> +indicated if RMIDs are not available.
> +
> +To specify monitoring on package 0 and package 1:
> +#echo 0-1 > /sys/fs/cgroup/perf_event/p1/perf_event.cqm_mon_mask
> +
> +An error is thrown if packages not online are specified.

I very much dislike both those for adding files to the perf cgroup.
Drivers should really not do that.

I absolutely hate the second because events already have affinity.

I can't see this happening.