Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755599AbZFLMcR (ORCPT ); Fri, 12 Jun 2009 08:32:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752010AbZFLMb7 (ORCPT ); Fri, 12 Jun 2009 08:31:59 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:51940 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750783AbZFLMb6 (ORCPT ); Fri, 12 Jun 2009 08:31:58 -0400 Date: Fri, 12 Jun 2009 14:31:52 +0200 From: Ingo Molnar To: Mike Frysinger Cc: Peter Zijlstra , Paul Mackerras , linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open when supported Message-ID: <20090612123152.GE31845@elte.hu> References: <1244806169-12232-1-git-send-email-vapier@gentoo.org> <20090612120507.GH16044@elte.hu> <8bd0f97a0906120513u4e823460t8192f00fd0460ab@mail.gmail.com> <20090612121757.GD31845@elte.hu> <8bd0f97a0906120522v51ae0151i48d5f6846ddcff10@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8bd0f97a0906120522v51ae0151i48d5f6846ddcff10@mail.gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2361 Lines: 52 * Mike Frysinger wrote: > On Fri, Jun 12, 2009 at 08:17, Ingo Molnar wrote: > > * Mike Frysinger wrote: > >> On Fri, Jun 12, 2009 at 08:05, Ingo Molnar wrote: > >> > * Mike Frysinger wrote: > >> >> If the port does not support HAVE_PERF_COUNTERS, then they can't > >> >> support the perf_counter_open syscall either. ?Rather than forcing > >> >> everyone to add an ignore (or suffer the warning until they get > >> >> around to implementing support), only whine about the syscall when > >> >> applicable. > >> > > >> > No, this patch is wrong - it's really easy to add support: just hook > >> > up the syscall. This should happen for every architecture really, so > >> > the warning is correct and it should not be patched out. > >> > > >> > PMU support is not required to get perfcounters support: if an > >> > architecture hooks up the syscall it will get generic software > >> > counters and the tools will work as well. > >> > > >> > Profiling falls back to a hrtimer-based sampling method - this is a > >> > much better fallback than oprofile's fall-back to the timer tick. > >> > This hrtimer based sampling is dynticks/nohz-correct and can go > >> > beyond HZ if the architecture supports hrtimers. > >> > >> if there is generic support available, why must every arch select > >> HAVE_PERF_COUNTERS in their Kconfig ? > > > > Because we only want to enable it on architectures that have tested > > it. It should only need a syscall addition, but nothing beats having > > tested things, hence we have that additional Kconfig symbol. > > that is a pretty weak reason. [...] It isnt - this is proper isolation - dont offer something to the user to enable that 1) cannot be used due to the lack of a syscall 2) has not been tested by anyone on that architecture, ever. That way say build breakages or runtime failures due to perfcounters only become possible on an architecture if the architecture maintainer has hooked up the syscall and has provided HAVE_PERF_COUNTERS explicitly. This is a basic engineering principle really. Ingo -- 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/