From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1750984AbdFSNjW (ORCPT <rfc822;w@1wt.eu>);
        Mon, 19 Jun 2017 09:39:22 -0400
Received: from foss.arm.com ([217.140.101.70]:49998 "EHLO foss.arm.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1750733AbdFSNjV (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 19 Jun 2017 09:39:21 -0400
Date: Mon, 19 Jun 2017 14:38:31 +0100
From: Mark Rutland <mark.rutland@arm.com>
To: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>, Kan Liang <kan.liang@intel.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@intel.com>,
        Valery Cherepennikov <valery.cherepennikov@intel.com>,
        David Carrillo-Cisneros <davidcc@google.com>,
        Stephane Eranian <eranian@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during
 per-process profiling of STREAM benchmark on Intel Xeon Phi
Message-ID: <20170619133831.GB3894@leverpostej>
References: <09226446-39b9-9bd2-d60f-b9bb947987c5@linux.intel.com>
 <20170615195618.GA8807@leverpostej>
 <07a76338-4c71-569a-d36e-7d6bcd10bd74@linux.intel.com>
 <20170616090938.GB20092@leverpostej>
 <f918eb9b-d856-a3ee-a76b-0aeca8141554@linux.intel.com>
 <22a2dafb-de05-199b-54ed-0c3b24349826@linux.intel.com>
 <20170619124639.GA3661@leverpostej>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170619124639.GA3661@leverpostej>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Jun 19, 2017 at 01:46:39PM +0100, Mark Rutland wrote:
> On Fri, Jun 16, 2017 at 05:22:29PM +0300, Alexey Budankov wrote:
> > On 16.06.2017 17:08, Alexey Budankov wrote:
> > >On 16.06.2017 12:09, Mark Rutland wrote:
> > >>There's a --per-thread option to ask perf record to not duplicate the
> > >>event per-cpu.
> > >>
> > >>If you use that, what amount of slowdown do you see?
> > 
> > After applying all three patches:
> > 
> > - system-wide collection:
> > 
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 303.795 MB perf.data (~13272985 samples) ]
> > 2162.08user 176.24system 0:12.97elapsed 18021%CPU (0avgtext+0avgdata
> > 1187208maxresident)k
> > 0inputs+622624outputs (0major+1360285minor)pagefaults 0swaps
> > 
> > - per-process collection:
> > 
> > [ perf record: Woken up 5 times to write data ]
> > [ perf record: Captured and wrote 1.079 MB perf.data (~47134 samples) ]
> > 2102.39user 153.88system 0:12.78elapsed 17645%CPU (0avgtext+0avgdata
> > 1187156maxresident)k
> > 0inputs+2272outputs (0major+1181660minor)pagefaults 0swaps
> > 
> > Elapsed times look similar. Data file sizes differ significantly.
> 
> Interesting. I wonder if that's because we're losing samples due to
> hammering the rb, or if that's a side-effect of this patch.
> 
> Does perf report describe any lost chunks?
> 
> For comparison, can you give --per-thread a go prior to these patches
> being applied?

FWIW, I had a go with (an old) perf record on an arm64 system using
--per-thread, and I see that no samples are recorded, which seems like a
bug.

With --per-thread, the slwodown was ~20%, whereas with the defaults it
was > 400%.

Thanks,
Mark.