Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965327AbaFSUpZ (ORCPT ); Thu, 19 Jun 2014 16:45:25 -0400 Received: from mail-oa0-f52.google.com ([209.85.219.52]:44579 "EHLO mail-oa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964975AbaFSUpY (ORCPT ); Thu, 19 Jun 2014 16:45:24 -0400 MIME-Version: 1.0 In-Reply-To: <20140619204041.GW8178@tassilo.jf.intel.com> References: <1403193509-22393-1-git-send-email-eranian@google.com> <1403193509-22393-2-git-send-email-eranian@google.com> <20140619180028.GU8178@tassilo.jf.intel.com> <20140619201801.GV8178@tassilo.jf.intel.com> <20140619204041.GW8178@tassilo.jf.intel.com> Date: Thu, 19 Jun 2014 22:45:23 +0200 Message-ID: Subject: Re: [PATCH 1/2] perf/x86: update Haswell PEBS event constraints From: Stephane Eranian To: Andi Kleen Cc: LKML , Peter Zijlstra , "mingo@elte.hu" , Joe Mario , Don Zickus , Jiri Olsa , Arnaldo Carvalho de Melo Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 19, 2014 at 10:40 PM, Andi Kleen wrote: > On Thu, Jun 19, 2014 at 10:31:29PM +0200, Stephane Eranian wrote: >> On Thu, Jun 19, 2014 at 10:18 PM, Andi Kleen wrote: >> >> I don't quite understand that. >> >> You need to know which events support PEBS. You need a table >> > >> > We're talking about the kernel allowing things here. >> > Yes the user still needs to know what supports PEBS, but >> > that doesn't concern the kernel. >> > >> Just need to make sure you don't return bogus information. > > GIGO. We only need to prevent security issues. > >> > You can just allow it for all, it's a nop if the event doesn't >> > support it. And also the fields like DataLA are simply 0 when >> > not supported. >> > >> >> Let's take a example. If I do resource_stalls:pp, the kernel >> will let it go through and clear the PMI bit on the config as >> is required for PEBS mode. The counter will count normally >> and never fire an interrupt, even when it overflows. It would >> never execute the PMI handler and thus never look at the >> PEBS content. You'd never get any samples. > > Yes if the user specifies a bogus raw event it will not count. > That's fine. The important part is just that nothing ever crashes. > That would certainly avoid the problem of missing events in pebs table. I had a problem with that just today. It also speed up scheduling as well by avoid the table lookups. Note that I will soon post a patch to speed up scheduling for all x86 processors. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/