From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758922Ab0CMOIZ (ORCPT ); Sat, 13 Mar 2010 09:08:25 -0500 Received: from fg-out-1718.google.com ([72.14.220.156]:42776 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757339Ab0CMOIY (ORCPT ); Sat, 13 Mar 2010 09:08:24 -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=JUsBNwoXHijMfcegp8jARamcE5waF4qsiI6Plwsj0dyfh9sZU9+q4IKHNrkOf0TgCi cxjmUrpbzX9ZmHcpQSKMi24w7gw88g8qBTMt4hP4qaTGe5f4eruMA4364m57T1y3hUXp 0iK2xzqgpa5UMOKNouG0OIR1A2e+K01FQtJ/s= Date: Sat, 13 Mar 2010 17:08:19 +0300 From: Cyrill Gorcunov To: Ingo Molnar Cc: Lin Ming , Peter Zijlstra , LKML Subject: Re: [PATCH] x86,perf: Unmask LVTPC only if we have APIC supported Message-ID: <20100313140819.GC18623@lenovo> References: <20100313081116.GA5179@lenovo> <20100313122432.GA10810@elte.hu> <20100313123256.GC5179@lenovo> <20100313124036.GA17769@elte.hu> <20100313134256.GB18623@lenovo> <20100313135022.GA4267@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100313135022.GA4267@elte.hu> 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 Sat, Mar 13, 2010 at 02:50:22PM +0100, Ingo Molnar wrote: [ ... ] > > > > > > 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 > > > > > > > Looking at code a bit and config deps I think the former proposal with > > #ifdef is minimal (in amount of changes) and sufficient. perf_event.c > > uses #ifdef CONFIG_X86_LOCAL_APIC for the very same reason. > > > > The former issue with config dependencies is that we may need to compile > > perf_event.c without CONFIG_LOCAL_APIC support at all (and this is a case > > for which you've posted the config). CONFIG_LOCAL_APIC deps on X86_UP_APIC, > > the config has no X86_UP_APIC support and as result -- no CONFIG_LOCAL_APIC > > and no apic.o compiled. > > > > So, as expected, no apic_write/read and friends there. We may introduce > > apic_write/read weak(s) but this would only mess the code more and would > > smell unpleasant I think :) . > > > > All-in-once: unresolved external symbol here, which could be fixed either by > > introducing dummy symbol, or conditional compilation. I think the second is > > preferred if the issue is just one line code. > > > > Or you mean something different and I took a wrong mind-path? > > Well it's not just one line of code as (like you mentioned) perf_event.c is > affected as well. > > Introducing a dummy (NOP) placeholder method is what we are doing in all the > other cases (such as spin_lock()), we dont pollute the kernel with #ifdefs. > > Ingo > ok, understood what you mean. will back with patch. -- Cyrill