From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753019Ab0CBNKO (ORCPT ); Tue, 2 Mar 2010 08:10:14 -0500 Received: from mail-bw0-f209.google.com ([209.85.218.209]:60748 "EHLO mail-bw0-f209.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752776Ab0CBNKL (ORCPT ); Tue, 2 Mar 2010 08:10:11 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=XNRrya74El7GKQIKM6RoFHg9gaJh3AD69pxbjrQ2NEXZZcKbf2MMhBl6pbLKBU5fzz OAjEE/JlAgTUqHy1nMvvUermQpXWMamftPVN2gbduEN0ksqN9JncxeKYrKZmVpIedP+0 xkFrSs4xfBBl9L+UcFchVdzGRb+WEuPkUa1QI= Date: Tue, 2 Mar 2010 14:10:05 +0100 From: Frederic Weisbecker To: eranian@google.com Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@elte.hu, paulus@samba.org, perfmon2-devel@lists.sf.net, robert.richter@amd.com, eranian@gmail.com Subject: Re: [PATCH] perf_events: add sampling period randomization support Message-ID: <20100302131002.GD5137@nowhere> References: <1267510029-19750-1-git-send-email-eranian@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1267510029-19750-1-git-send-email-eranian@google.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 01, 2010 at 10:07:09PM -0800, eranian@google.com wrote: > This patch adds support for randomizing the sampling period. > Randomization is very useful to mitigate the bias that exists > with sampling. The random number generator does not need to > be sophisticated. This patch uses the builtin random32() > generator. > > The user activates randomization by setting the perf_event_attr.random > field to 1 and by passing a bitmask to control the range of variation > above the base period. Period will vary from period to period & mask. > Note that randomization is not available when a target interrupt rate > (freq) is enabled. > > The last used period can be collected using the PERF_SAMPLE_PERIOD flag > in sample_type. > > The patch has been tested on X86. There is also code for PowerPC but > I could not test it. > > Signed-off-by: Stephane Eranian > > -- > arch/powerpc/kernel/perf_event.c | 3 +++ > arch/x86/kernel/cpu/perf_event.c | 2 ++ > arch/x86/kernel/cpu/perf_event_intel.c | 4 ++++ > include/linux/perf_event.h | 7 +++++-- > kernel/perf_event.c | 24 ++++++++++++++++++++++++ > 5 files changed, 38 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c > index b6cf8f1..994df17 100644 > --- a/arch/powerpc/kernel/perf_event.c > +++ b/arch/powerpc/kernel/perf_event.c > @@ -1150,6 +1150,9 @@ static void record_and_restart(struct perf_event *event, unsigned long val, > val = 0; > left = atomic64_read(&event->hw.period_left) - delta; > if (period) { > + if (event->attr.random) > + perf_randomize_event_period(event); > + > if (left <= 0) { > left += period; > if (left <= 0) > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index 641ccb9..159d951 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -1110,6 +1110,8 @@ static int x86_pmu_handle_irq(struct pt_regs *regs) > if (val & (1ULL << (x86_pmu.event_bits - 1))) > continue; > > + if (event->attr.random) > + perf_randomize_event_period(event); > /* > * event overflow > */ > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c > index cf6590c..5c8d6ed 100644 > --- a/arch/x86/kernel/cpu/perf_event_intel.c > +++ b/arch/x86/kernel/cpu/perf_event_intel.c > @@ -690,6 +690,10 @@ static int intel_pmu_save_and_restart(struct perf_event *event) > int ret; > > x86_perf_event_update(event, hwc, idx); > + > + if (event->attr.random) > + perf_randomize_event_period(event); > + > ret = x86_perf_event_set_period(event, hwc, idx); > > return ret; > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 04f06b4..e91a759 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -203,8 +203,8 @@ struct perf_event_attr { > enable_on_exec : 1, /* next exec enables */ > task : 1, /* trace fork/exit */ > watermark : 1, /* wakeup_watermark */ > - > - __reserved_1 : 49; > + random : 1, /* period randomization */ I'd rather name this field random_period. Even though the comment tell us enough, it's better that the code speak for itself.