Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754071AbZCQM6U (ORCPT ); Tue, 17 Mar 2009 08:58:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755166AbZCQM6K (ORCPT ); Tue, 17 Mar 2009 08:58:10 -0400 Received: from mga02.intel.com ([134.134.136.20]:6248 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752639AbZCQM6I convert rfc822-to-8bit (ORCPT ); Tue, 17 Mar 2009 08:58:08 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.38,378,1233561600"; d="scan'208";a="395160899" From: "Metzger, Markus T" To: Ingo Molnar CC: "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "hpa@zytor.com" , "markus.t.metzger@gmail.com" , "roland@redhat.com" , "eranian@googlemail.com" , "oleg@redhat.com" , "Villacis, Juan" , "ak@linux.jf.intel.com" Date: Tue, 17 Mar 2009 12:57:39 +0000 Subject: RE: [patch 1/5] x86, bts: detect size of DS fields Thread-Topic: [patch 1/5] x86, bts: detect size of DS fields Thread-Index: Acmm/NOiijrhTk/gSoehVHQcmoTHDAAAEWlw Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E4A6642C7@irsmsx504.ger.corp.intel.com> References: <20090313104218.A30096@sedona.ch.intel.com> <20090313110357.GC31094@elte.hu> <928CFBE8E7CB0040959E56B4EA41A77E4A663C47@irsmsx504.ger.corp.intel.com> <20090317105558.GK6477@elte.hu> <928CFBE8E7CB0040959E56B4EA41A77E4A664285@irsmsx504.ger.corp.intel.com> <20090317123442.GB22759@elte.hu> In-Reply-To: <20090317123442.GB22759@elte.hu> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-cr-hashedpuzzle: AZr2 EyUD Y6rN nwMq qXqK qjtp rmfF 2Bed 2I0p +5N5 AABBrA== ABAgHw== ABvBLQ== AB8inw== ADzl4Q== AJdPcA==;9;YQBrAEAAbABpAG4AdQB4AC4AagBmAC4AaQBuAHQAZQBsAC4AYwBvAG0AOwBlAHIAYQBuAGkAYQBuAEAAZwBvAG8AZwBsAGUAbQBhAGkAbAAuAGMAbwBtADsAaABwAGEAQAB6AHkAdABvAHIALgBjAG8AbQA7AGwAaQBuAHUAeAAtAGsAZQByAG4AZQBsAEAAdgBnAGUAcgAuAGsAZQByAG4AZQBsAC4AbwByAGcAOwBtAGEAcgBrAHUAcwAuAHQALgBtAGUAdAB6AGcAZQByAEAAZwBtAGEAaQBsAC4AYwBvAG0AOwBtAGkAbgBnAG8AQABlAGwAdABlAC4AaAB1ADsAbwBsAGUAZwBAAHIAZQBkAGgAYQB0AC4AYwBvAG0AOwByAG8AbABhAG4AZABAAHIAZQBkAGgAYQB0AC4AYwBvAG0AOwB0AGcAbAB4AEAAbABpAG4AdQB0AHIAbwBuAGkAeAAuAGQAZQA=;Sosha1_v1;7;{44E790CA-160B-4DCD-B339-388149263F37};bQBhAHIAawB1AHMALgB0AC4AbQBlAHQAegBnAGUAcgBAAGkAbgB0AGUAbAAuAGMAbwBtAA==;Tue, 17 Mar 2009 12:57:39 GMT;UgBFADoAIABbAHAAYQB0AGMAaAAgADEALwA1AF0AIAB4ADgANgAsACAAYgB0AHMAOgAgAGQAZQB0AGUAYwB0ACAAcwBpAHoAZQAgAG8AZgAgAEQAUwAgAGYAaQBlAGwAZABzAA== x-cr-puzzleid: {44E790CA-160B-4DCD-B339-388149263F37} acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2686 Lines: 78 >-----Original Message----- >From: Ingo Molnar [mailto:mingo@elte.hu] >Sent: Tuesday, March 17, 2009 1:35 PM >To: Metzger, Markus T >> I think I found the problem: >> ds_request_bts() needs to allocate a small amount of memory. >> It uses GFP_KERNEL. >> >> Hw-branch-tracer essentially does on_each_cpu(ds_request_bts()). >> >> Since ds_request_bts() is meant to be called on the cpu that >> should be traced, it should use GFP_ATOMIC to allow calls from >> smp_call_function() and friends. >> >> Would that be acceptable? > >That's not really a good solution - GFP_ATOMIC is not a reliable >form of allocation. In that case, I would need to double the interface. So far, I used task == NULL to indicate tracing on the current cpu. I could turn this into: ds_request_bts_task(struct task_struct *task, ....) and ds_request_bts_cpu(int cpu, ....) This way, I could do the allocation using GFP_KERNEL and then do the wrmsrl() to enable tracing using smp_call_function(). Does that sound better? >the other callsites are buggy too: > > smp_call_function_single(cpu, bts_trace_start_cpu, NULL, 1); > >done under the bts_tracer_lock in addition to an atomic IPI >context. That lock synchronizes the on_each_cpu initialization calls with the hotplug handler. The for_each_online_cpu iteration in smp_call_function_many() may race with the smp_call_function_single() when a new cpu arrives or departs. >for_each_online_cpu() done under the mutex would be better i >guess, plus you can allocate any memory before you do the SMP >cross-call, and pass it to the IPI handler via the data >parameter. (NULL in the sequence above) The memory is allocated by ds_request_bts(). It holds the tracer struct returned to the caller. The struct is private to ds.c. regards, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. 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