From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id 07D1AB7080 for ; Tue, 4 Aug 2009 03:06:48 +1000 (EST) Received: from e6.ny.us.ibm.com (e6.ny.us.ibm.com [32.97.182.146]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e6.ny.us.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 69839DDD04 for ; Tue, 4 Aug 2009 03:06:44 +1000 (EST) Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e6.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id n73HAODv028357 for ; Mon, 3 Aug 2009 13:10:24 -0400 Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id n73H6dPh240476 for ; Mon, 3 Aug 2009 13:06:39 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n73H6cKO003285 for ; Mon, 3 Aug 2009 13:06:39 -0400 Subject: Re: [PATCH 3/20] powerpc/mm: Add HW threads support to no_hash TLB management From: Dave Kleikamp To: Kumar Gala In-Reply-To: <2EA75185-AC33-4BCA-AE53-A60E6D98DC46@kernel.crashing.org> References: <20090724091523.8AD8CDDD1B@ozlabs.org> <2E027F3C-8FAA-42EC-99B2-9B7EC470094E@kernel.crashing.org> <6FD94305-B60D-4DAF-8296-88345D11187F@kernel.crashing.org> <1249079342.1509.99.camel@pasglop> <1249265010.5516.31.camel@concordia> <2EA75185-AC33-4BCA-AE53-A60E6D98DC46@kernel.crashing.org> Content-Type: text/plain Date: Mon, 03 Aug 2009 12:06:37 -0500 Message-Id: <1249319197.6192.3.camel@norville.austin.ibm.com> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2009-08-03 at 11:21 -0500, Kumar Gala wrote: > On Aug 2, 2009, at 9:03 PM, Michael Ellerman wrote: > > > On Sat, 2009-08-01 at 08:29 +1000, Benjamin Herrenschmidt wrote: > >> On Thu, 2009-07-30 at 22:35 -0500, Kumar Gala wrote: > >>>> /* XXX This clear should ultimately be part of > >>> local_flush_tlb_mm */ > >>>> - __clear_bit(id, stale_map[cpu]); > >>>> + for (cpu = cpu_first_thread_in_core(cpu); > >>>> + cpu <= cpu_last_thread_in_core(cpu); cpu++) > >>>> + __clear_bit(id, stale_map[cpu]); > >>>> } > >>> > >>> This looks a bit dodgy. using 'cpu' as both the loop variable and > >>> what you are computing to determine loop start/end.. > >>> > >> Hrm... I would have thought that it was still correct... do you see > >> any > >> reason why the above code is wrong ? because if not we may be > >> hitting a > >> gcc issue... > >> > >> IE. At loop init, cpu gets clamped down to the first thread in the > >> core, > >> which should be fine. Then, we compare CPU to the last thread in core > >> for the current CPU which should always return the same value. > >> > >> So I'm very interested to know what is actually wrong, ie, either I'm > >> just missing something obvious, or you are just pushing a bug under > >> the > >> carpet which could come back and bit us later :-) > > > > for (cpu = cpu_first_thread_in_core(cpu); > > cpu <= cpu_last_thread_in_core(cpu); cpu++) > > __clear_bit(id, stale_map[cpu]); > > > > == > > > > cpu = cpu_first_thread_in_core(cpu); > > while (cpu <= cpu_last_thread_in_core(cpu)) { > > __clear_bit(id, stale_map[cpu]); > > cpu++; > > } cpu_last_thread_in_core(cpu) is a moving target. You want something like: cpu = cpu_first_thread_in_core(cpu); last = cpu_last_thread_in_core(cpu); while (cpu <= last) { __clear_bit(id, stale_map[cpu]); cpu++; } > > > > cpu = 0 > > cpu <= 1 > > cpu++ (1) > > cpu <= 1 > > cpu++ (2) > > cpu <= 3 > > ... > > Which is pretty much what I see, in a dual core setup, I get an oops > because we are trying to clear cpu #2 (which clearly doesn't exist) > > cpu = 1 > (in loop) > clearing 1 > clearing 2 > OOPS > > - k -- David Kleikamp IBM Linux Technology Center