From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423743AbcBQQ3O (ORCPT ); Wed, 17 Feb 2016 11:29:14 -0500 Received: from pegase1.c-s.fr ([93.17.236.30]:61855 "EHLO mailhub1.si.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423724AbcBQQ3L (ORCPT ); Wed, 17 Feb 2016 11:29:11 -0500 Subject: Re: [PATCH v5] powerpc32: provide VIRT_CPU_ACCOUNTING To: Scott Wood References: <20160211161650.1F12C1A2400@localhost.localdomain> <1455657664.2463.68.camel@buserror.net> Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org From: Christophe Leroy Message-ID: <56C49FD3.8060108@c-s.fr> Date: Wed, 17 Feb 2016 17:29:07 +0100 User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <1455657664.2463.68.camel@buserror.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 16/02/2016 22:21, Scott Wood a écrit : > On Thu, 2016-02-11 at 17:16 +0100, Christophe Leroy wrote: >> This patch provides VIRT_CPU_ACCOUTING to PPC32 architecture. >> PPC32 doesn't have the PACA structure, so we use the task_info >> structure to store the accounting data. >> >> In order to reuse on PPC32 the PPC64 functions, all u64 data has >> been replaced by 'unsigned long' so that it is u32 on PPC32 and >> u64 on PPC64 >> >> Signed-off-by: Christophe Leroy >> --- >> Changes in v3: unlike previous version of the patch that was inspired >> from IA64 architecture, this new version tries to reuse as much as >> possible the PPC64 implementation. >> >> PPC32 doesn't have PACA and past discusion on v2 version has shown >> that it is not worth implementing a PACA in PPC32 architecture >> (see below benh opinion) >> >> benh: PACA is actually a data structure and you really really don't want it >> on ppc32 :-) Having a register point to current works, having a register >> point to per-cpu data instead works too (ie, change what we do today), >> but don't introduce a PACA *please* :-) > And Ben never replied to my reply at the time: > > "What is special about 64-bit that warrants doing things differently from 32 > -bit? What is the difference between PACA and "per-cpu data", other than the > obscure name?" > > I can understand wanting to avoid churn, but other than that, doing things > differently on 64-bit versus 32-bit sucks. > What I can see is that PACA is always available via register r13. Do we have anything equivalent on PPC32 ? If we define a per-cpu data for accounting, what will be the quick way to get access to it in entry_32.S ? Something like a table of accounting data for each CPU, that we index with thread_info->cpu ? This would allow a quite quick access, is it the good way to proceed in order to have something closer to PPC64 ? Christophe