Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752438AbZCQOwi (ORCPT ); Tue, 17 Mar 2009 10:52:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752100AbZCQOw2 (ORCPT ); Tue, 17 Mar 2009 10:52:28 -0400 Received: from mga09.intel.com ([134.134.136.24]:51937 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752049AbZCQOw1 convert rfc822-to-8bit (ORCPT ); Tue, 17 Mar 2009 10:52:27 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.38,379,1233561600"; d="scan'208";a="498461171" 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 14:51:20 +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/gSoehVHQcmoTHDAAAEWlwAARtJQA= Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E4A6643E0@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> <928CFBE8E7CB0040959E56B4EA41A77E4A6642C7@irsmsx504.ger.corp.intel.com> In-Reply-To: <928CFBE8E7CB0040959E56B4EA41A77E4A6642C7@irsmsx504.ger.corp.intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: 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: 2984 Lines: 91 >-----Original Message----- >From: Metzger, Markus T >Sent: Tuesday, March 17, 2009 1:58 PM >To: Ingo Molnar >>> 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. That problem also is in the .29-rc version. It affects the hw-branch-tracer. The ptrace interface should not be affected. The changes I sketched below will be too intrusive. Do you want a small patch that turns GFP_KERNEL into GFP_ATOMIC for .29? regards, markus. >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. If you are not the intended recipient, please contact the sender and delete all copies. -- 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/