From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754844Ab1I1P35 (ORCPT ); Wed, 28 Sep 2011 11:29:57 -0400 Received: from mx2.parallels.com ([64.131.90.16]:53288 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752938Ab1I1P34 (ORCPT ); Wed, 28 Sep 2011 11:29:56 -0400 Message-ID: <4E833D27.50906@parallels.com> Date: Wed, 28 Sep 2011 12:28:39 -0300 From: Glauber Costa User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2 MIME-Version: 1.0 To: Martin Schwidefsky CC: Peter Zijlstra , , , , , , Heiko Carstens Subject: Re: [RFD 4/9] Make total_forks per-cgroup References: <1316816432-9237-1-git-send-email-glommer@parallels.com> <1316816432-9237-5-git-send-email-glommer@parallels.com> <1317160837.21836.21.camel@twins> <20110928101357.5a90c2ab@de.ibm.com> <1317206124.20318.6.camel@twins> <20110928144218.6a4882e5@de.ibm.com> In-Reply-To: <20110928144218.6a4882e5@de.ibm.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [187.46.219.221] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/28/2011 09:42 AM, Martin Schwidefsky wrote: > On Wed, 28 Sep 2011 12:35:24 +0200 > Peter Zijlstra wrote: > >> On Wed, 2011-09-28 at 10:13 +0200, Martin Schwidefsky wrote: >>> On Wed, 28 Sep 2011 00:00:37 +0200 >>> Peter Zijlstra wrote: >>> >>>> On Fri, 2011-09-23 at 19:20 -0300, Glauber Costa wrote: >>>>> @@ -1039,6 +1035,8 @@ static void posix_cpu_timers_init(struct task_struct *tsk) >>>>> INIT_LIST_HEAD(&tsk->cpu_timers[2]); >>>>> } >>>>> >>>>> +struct task_group *task_group(struct task_struct *p); >>>> >>>> That doesn't appear to be actually used in this file.. >>>> >>>> Also, since there's already a for_each_possible_cpu() loop in that >>>> proc/stat function, would it yield some code improvement to make >>>> total_forks a cpu_usage_stat? >>>> >>>> I guess the whole cputime64_t crap gets in the way of that being >>>> natural... >>>> >>>> We could of course kill off the cputime64_t thing, its pretty pointless >>>> and its a u64 all over the board. I think Martin or Heiko created this >>>> stuff (although I might be wrong, my git tree doesn't go back that far). >>> >>> The reason to introduce cputime_t has been that different architecture >>> needed differently sized integers for their respective representation >>> of cputime. On x86-32 the number of ticks is recorded in a u32, on s390 >>> we needed a u64 for the cpu timer values. cputime64_t is needed for >>> cpustat and other sums of cputime that would overflow a cputime_t >>> (in particular on x86-32 with the u32 cputime_t and the u64 cputime64_t). >>> >>> Now we would convert everything to u64 but that would cause x86-32 to >>> use 64-bit arithmetic for the tick counter. If that is acceptable I >>> can't say. >> >> Right, so the main point was about cputime64_t, we might as well use a >> u64 for that throughout and ditch the silly cputime64_$op() accessors >> and write normal code. >> >> But even if cputime_t differs between 32 and 64 bit machines, there is >> no reason actually use cputime_add(), C can do this. >> >> The only reason to use things like cputime_add() is if you use a non >> simple type, but that doesn't seem to be the case. >> >> So I think we can simplify the code lots by doing away with cputime64_t >> and all the cputime_*() functions. We can keep cputime_t, or we can use >> unsigned long, which I think will end up doing pretty much the same. >> >> That is, am I missing some added value of all this cputime*() foo? > > C can do the math as long as the encoding of the cputime is simple enough. > Can we demand that a cputime value needs to be an integral type ? > > What I did when I wrote all that stuff is to define cputime_t as a struct > that contains a single u64. That way I found all the places in the kernel > that used a cputime and could convert the code accordingly. > > My fear is that if the cputime_xxx operations are removed, code will > sneak in again that just uses an unsigned long instead of a cputime_t. > That would break any arch that requires something bigger than a u32 for > its cputime. I really have to find my old debugging patch and see if we > already have bit rot in regard to cputime_t. > Martin, Proposal is to keep cputime_t as is, and only get rid of its size-specific version. So I think we're safe as far as cputime_t is concerned.