From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759110Ab0CMMk6 (ORCPT ); Sat, 13 Mar 2010 07:40:58 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:40188 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758828Ab0CMMky (ORCPT ); Sat, 13 Mar 2010 07:40:54 -0500 Date: Sat, 13 Mar 2010 13:40:36 +0100 From: Ingo Molnar To: Cyrill Gorcunov Cc: Lin Ming , Peter Zijlstra , LKML Subject: Re: [PATCH] x86,perf: Unmask LVTPC only if we have APIC supported Message-ID: <20100313124036.GA17769@elte.hu> References: <20100313081116.GA5179@lenovo> <20100313122432.GA10810@elte.hu> <20100313123256.GC5179@lenovo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100313123256.GC5179@lenovo> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=none autolearn=no SpamAssassin version=3.2.5 _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Cyrill Gorcunov wrote: > On Sat, Mar 13, 2010 at 01:24:32PM +0100, Ingo Molnar wrote: > > > > * Cyrill Gorcunov wrote: > > > > > Ingo reported > > > | > > > | There's a build failure on -tip with the P4 driver, on UP 32-bit, if > > > | PERF_EVENTS is enabled but UP_APIC is disabled: > > > | > > > | arch/x86/built-in.o: In function `p4_pmu_handle_irq': > > > | perf_event.c:(.text+0xa756): undefined reference to `apic' > > > | perf_event.c:(.text+0xa76e): undefined reference to `apic' > > > | > > > > > > So we have to unmask LVTPC only if we're configured to have one. > > > > > > Reported-by: Ingo Molnar > > > CC: Lin Ming > > > CC: Peter Zijlstra > > > Signed-off-by: Cyrill Gorcunov > > > --- > > > arch/x86/kernel/cpu/perf_event_p4.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > ===================================================================== > > > --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c > > > +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c > > > @@ -365,8 +365,10 @@ static int p4_pmu_handle_irq(struct pt_r > > > } > > > > > > if (handled) { > > > +#ifdef CONFIG_X86_LOCAL_APIC > > > /* p4 quirk: unmask it again */ > > > apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED); > > > +#endif > > > inc_irq_stat(apic_perf_irqs); > > > > This ugly #ifdef looks like a workaround though. Why doesnt apic_write() map > > to nothing in that case? > > > > Ingo > > > > It is. I mean -- it maps to nothing if apic is disabled. But the scenario is > that no apic configured at all. Actually I wonder how this code is supposed > to work without apic support. > > Pehpaps better to make a p4 quirk helper here, since #ifdef at this point > looks ugly indeed. > > Don't apply it then. Will back with other solution. apic_write() is really just equivalent to a spin_lock() on UP without UP_IOAPIC set - it should do nothing. So if it does something and fails the build, then that should be fixed - not the P4 PMU code. Ingo