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 S1751946AbdFSO7M (ORCPT <rfc822;w@1wt.eu>);
        Mon, 19 Jun 2017 10:59:12 -0400
Received: from mga03.intel.com ([134.134.136.65]:39669 "EHLO mga03.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751113AbdFSO7K (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 19 Jun 2017 10:59:10 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.39,361,1493708400"; 
   d="scan'208";a="1184349620"
Date: Mon, 19 Jun 2017 07:59:08 -0700
From: Andi Kleen <ak@linux.intel.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@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: <20170619145908.GA23705@tassilo.jf.intel.com>
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>
 <20170619133831.GB3894@leverpostej>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170619133831.GB3894@leverpostej>
User-Agent: Mutt/1.8.0 (2017-02-23)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> > 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%.

I'm not sure what the point of the experiment is? It has to work
with reasonable overead even without --per-thread.

FWIW Alexey already root caused the problem, so there's no need
to restart the debugging.

-Andi