From: Andi Kleen <andi@firstfloor.org>
To: David Carrillo-Cisneros <davidcc@google.com>
Cc: Andi Kleen <andi@firstfloor.org>,
Shivappa Vikas <vikas.shivappa@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Vikas Shivappa <vikas.shivappa@linux.intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
"Luck, Tony" <tony.luck@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Stephane Eranian <eranian@google.com>,
hpa@zytor.com
Subject: Re: [PATCH 01/14] x86/cqm: Intel Resource Monitoring Documentation
Date: Tue, 27 Dec 2016 15:10:49 -0800 [thread overview]
Message-ID: <20161227231049.GT26852@two.firstfloor.org> (raw)
In-Reply-To: <CALcN6mjDo-0bqZb1ePrWXkAhVbe2TBAvadM3xqEyscovZCQoWQ@mail.gmail.com>
On Tue, Dec 27, 2016 at 01:33:46PM -0800, David Carrillo-Cisneros wrote:
> When using one intel_cmt/llc_occupancy/ cgroup perf_event in one CPU, the
> avg time to do __perf_event_task_sched_out + __perf_event_task_sched_in is
> ~1170ns
>
> most of the time is spend in cgroup ctx switch (~1120ns) .
>
> When using continuous monitoring in CQM driver, the avg time to
> find the rmid to write inside of pqr_context switch is ~16ns
>
> Note that this excludes the MSR write. It's only the overhead of
> finding the RMID
> to write in PQR_ASSOC. Both paths call the same routine to find the
> RMID, so there are
> about 1100 ns of overhead in perf_cgroup_switch. By inspection I assume most
> of it comes from iterating over the pmu list.
Do Kan's pmu list patches help?
https://patchwork.kernel.org/patch/9420035/
>
> > Or is there some other overhead other than the MSR write
> > you're concerned about?
>
> No, that problem is solved with the PQR software cache introduced in the series.
So it's already fixed?
How much is the cost with your cache?
>
>
> > Perhaps some optimization could be done in the code to make it faster,
> > then the new interface wouldn't be needed.
>
> There are some. One in my list is to create a list of pmus with at
> least one cgroup event
> and use it to iterate over in perf_cgroup_switch, instead of using the
> "pmus" list.
> The pmus list has grown a lot recently with the addition of all the uncore pmus.
Kan's patches above already do that I believe.
>
> Despite this optimization, it's unlikely that the whole sched_out +
> sched_in gets that
> close to the 15 ns of the non perf_event approach.
It would be good to see how close we can get. I assume
there is more potential for optimizations and fast pathing.
-Andi
next prev parent reply other threads:[~2016-12-27 23:10 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-16 23:12 [PATCH V4 00/14] Cqm2: Intel Cache Monitoring fixes and enhancements Vikas Shivappa
2016-12-16 23:12 ` [PATCH 01/14] x86/cqm: Intel Resource Monitoring Documentation Vikas Shivappa
2016-12-23 12:32 ` Peter Zijlstra
2016-12-23 19:35 ` Shivappa Vikas
2016-12-23 20:33 ` Peter Zijlstra
2016-12-23 21:41 ` Shivappa Vikas
2016-12-25 1:51 ` Shivappa Vikas
2016-12-27 7:13 ` David Carrillo-Cisneros
2016-12-27 20:00 ` Andi Kleen
2016-12-27 20:21 ` Shivappa Vikas
2016-12-27 21:38 ` David Carrillo-Cisneros
2016-12-27 21:33 ` David Carrillo-Cisneros
2016-12-27 23:10 ` Andi Kleen [this message]
2016-12-28 1:23 ` David Carrillo-Cisneros
2016-12-28 20:03 ` Shivappa Vikas
2016-12-16 23:12 ` [PATCH 02/14] x86/cqm: Remove cqm recycling/conflict handling Vikas Shivappa
2016-12-16 23:12 ` [PATCH 03/14] x86/rdt: Add rdt common/cqm compile option Vikas Shivappa
2016-12-16 23:12 ` [PATCH 04/14] x86/cqm: Add Per pkg rmid support Vikas Shivappa
2016-12-16 23:12 ` [PATCH 05/14] x86/cqm,perf/core: Cgroup support prepare Vikas Shivappa
2016-12-16 23:13 ` [PATCH 06/14] x86/cqm: Add cgroup hierarchical monitoring support Vikas Shivappa
2016-12-16 23:13 ` [PATCH 07/14] x86/rdt,cqm: Scheduling support update Vikas Shivappa
2016-12-16 23:13 ` [PATCH 08/14] x86/cqm: Add support for monitoring task and cgroup together Vikas Shivappa
2016-12-16 23:13 ` [PATCH 09/14] x86/cqm: Add Continuous cgroup monitoring Vikas Shivappa
2016-12-16 23:13 ` [PATCH 10/14] x86/cqm: Add RMID reuse Vikas Shivappa
2016-12-16 23:13 ` [PATCH 11/14] x86/cqm: Add failure on open and read Vikas Shivappa
2016-12-23 11:58 ` David Carrillo-Cisneros
2016-12-16 23:13 ` [PATCH 12/14] perf/core,x86/cqm: Add read for Cgroup events,per pkg reads Vikas Shivappa
2016-12-16 23:13 ` [PATCH 13/14] perf/stat: fix bug in handling events in error state Vikas Shivappa
2016-12-16 23:13 ` [PATCH 14/14] perf/stat: revamp read error handling, snapshot and per_pkg events Vikas Shivappa
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