From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757094Ab2IDNfi (ORCPT ); Tue, 4 Sep 2012 09:35:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39233 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752958Ab2IDNfh (ORCPT ); Tue, 4 Sep 2012 09:35:37 -0400 Date: Tue, 4 Sep 2012 09:35:29 -0400 From: Vivek Goyal To: Tao Ma Cc: linux-kernel@vger.kernel.org, Tejun Heo , Jens Axboe Subject: Re: [PATCH V2] block/throttle: Add IO throttled information in blkio.throttle. Message-ID: <20120904133528.GB13768@redhat.com> References: <1346390109-3169-1-git-send-email-tm@tao.ma> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1346390109-3169-1-git-send-email-tm@tao.ma> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 31, 2012 at 01:15:09PM +0800, Tao Ma wrote: [..] > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > index 1588c2d..9317d71 100644 > --- a/block/blk-throttle.c > +++ b/block/blk-throttle.c > @@ -46,6 +46,8 @@ struct tg_stats_cpu { > struct blkg_rwstat service_bytes; > /* total IOs serviced, post merge */ > struct blkg_rwstat serviced; > + /* total IOs queued, not submitted to the underlying device. */ > + struct blkg_rwstat io_queued; > }; Couple of questions. - blkg_rwstat is "unsigned" and io_queued can go negative too (Because throttled bio can very well be dispatched from other cpu from a worker thread). So is it a good idea to represent a negative number with unsingned type? - As this stat is per cpu, a reader might very well see negative (or a huge unsigned value) as number of io_queued. Not sure if that is acceptable. How would user space come to know whether it is a valid value or not. I thought per cpu stats are good for continuously increasing values but not necessarily for values which can increase as well as decrease. Thanks Vivek