Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757610AbZFLNWS (ORCPT ); Fri, 12 Jun 2009 09:22:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751843AbZFLNWF (ORCPT ); Fri, 12 Jun 2009 09:22:05 -0400 Received: from yw-out-2324.google.com ([74.125.46.28]:49349 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751302AbZFLNWD convert rfc822-to-8bit (ORCPT ); Fri, 12 Jun 2009 09:22:03 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=d4Dg8sb36aO+jdVCfXSclBIamzJB9s6YSn6ST+iUi2lcXzmGjMX6Ghbf7kc/woCGL/ HbsQrdwKsh5AoR7IAiYaUg8qSiZChxrHcDFPDsEQNgoS5+6cCT+zVWxw4Y0bJzxwDfyI noN44uvryhHLbLPZkLFOX6IADNKWVIKJg9sNw= MIME-Version: 1.0 In-Reply-To: <20090612130949.GJ31845@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> <20090612123152.GE31845@elte.hu> <8bd0f97a0906120541x739b7902pe40ff7aa91337bac@mail.gmail.com> <20090612125941.GI31845@elte.hu> <8bd0f97a0906120604o1e90ac93l469e86173224364e@mail.gmail.com> <20090612130949.GJ31845@elte.hu> From: Mike Frysinger Date: Fri, 12 Jun 2009 09:21:45 -0400 Message-ID: <8bd0f97a0906120621o609d7489v83cd3efc0102412d@mail.gmail.com> Subject: Re: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open when supported To: Ingo Molnar Cc: Peter Zijlstra , Paul Mackerras , linux-kernel@vger.kernel.org, Thomas Gleixner Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4437 Lines: 90 On Fri, Jun 12, 2009 at 09:09, Ingo Molnar wrote: > * Mike Frysinger wrote: >> On Fri, Jun 12, 2009 at 08:59, Ingo Molnar wrote: >> > * Mike Frysinger wrote: >> >> On Fri, Jun 12, 2009 at 08:31, Ingo Molnar wrote: >> >> > * 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. >> >> >> >> except that the syscall presence is trivial to detect in the code by >> >> something like: >> >> #ifndef __NR_perf_counter_open >> >> # error sorry, your arch has not hooked up perf_counter_open syscall yet >> >> #endif >> >> >> >> as for "no arch testing yet", there are plenty of drivers which lack >> >> arch depends in the Kconfig specifically so that it can be *easily* >> >> tested on random systems out there without requiring manual twiddling. >> > >> > This is a new kernel subsystem, not just yet another driver. >> >> so what ?  if it has generic pieces, it is exactly the same as yet >> another generic driver.  people should be able to randomly test >> build it when possible to discover latent issues that your testing >> limited to one arch did not find. >> >> > Which bit of: "we dont want perfcounters to be enabled in the >> > Kconfig on architectures that have no syscalls and no testing for >> > it" is hard to understand? It is a valid technical concern. >> >> your (1) is valid but i already pointed out a simple fix for that. >> your (2) is not. > > Uhm, your 'fix': > >  #ifndef __NR_perf_counter_open >  # error sorry, your arch has not hooked up perf_counter_open syscall yet >  #endif > > is completely unacceptable. We dont propagate build failures via > user-enable config options, we never did. There's a lot of people > doing randconfig builds - if it randomly failed due to your 'fix' > that would upset a lot of testing for no good reason. accept that is a valid bug: the arch is missing the syscall and it should hook it up -mike -- 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/