From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx113.postini.com [74.125.245.113]) by kanga.kvack.org (Postfix) with SMTP id AB6826B0133 for ; Tue, 30 Apr 2013 13:48:36 -0400 (EDT) Subject: Re: [PATCH 1/2] Make the batch size of the percpu_counter configurable From: Tim Chen In-Reply-To: <0000013e5bfd1548-a6ef7962-7b00-495b-8e83-d7a08413e165-000000@email.amazonses.com> References: <0000013e5b24d2c5-9b899862-e2fd-4413-8094-4f1e5a0c0f62-000000@email.amazonses.com> <1367339009.27102.174.camel@schen9-DESK> <0000013e5bfd1548-a6ef7962-7b00-495b-8e83-d7a08413e165-000000@email.amazonses.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 30 Apr 2013 10:48:14 -0700 Message-ID: <1367344094.27102.182.camel@schen9-DESK> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Andrew Morton , Tejun Heo , Al Viro , Dave Hansen , Andi Kleen , linux-kernel , linux-mm On Tue, 2013-04-30 at 17:28 +0000, Christoph Lameter wrote: > On Tue, 30 Apr 2013, Tim Chen wrote: > > > On Tue, 2013-04-30 at 13:32 +0000, Christoph Lameter wrote: > > > On Mon, 29 Apr 2013, Tim Chen wrote: > > > > > > > diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h > > > > index d5dd465..5ca7df5 100644 > > > > --- a/include/linux/percpu_counter.h > > > > +++ b/include/linux/percpu_counter.h > > > > @@ -22,6 +22,7 @@ struct percpu_counter { > > > > struct list_head list; /* All percpu_counters are on a list */ > > > > #endif > > > > s32 __percpu *counters; > > > > + int *batch ____cacheline_aligned_in_smp; > > > > }; > > > > > > What is this for and why does it have that alignmend? > > > > I was assuming that if batch is frequently referenced, it probably > > should not share a cache line with the counters field. > > And why is it a pointer? A pointer because the default percpu_counter_batch value could change later when cpus come online after we initialize per cpu counter and percpu_counter_batch will get computed again in percpu_counter_startup. Making it a pointer will make it unnecessary to come back and change the batch sizes if we use static batch value and default batch size. > > And the pointer is so frequently changed that it needs it own cache line? > On second thought, your're right. It is unnecessary for *batch to have its own cache line as the counters pointer and head_list above it will not change frequently. I'll remove the cache alignment. Tim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org