Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757404AbZLITo6 (ORCPT ); Wed, 9 Dec 2009 14:44:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756814AbZLITox (ORCPT ); Wed, 9 Dec 2009 14:44:53 -0500 Received: from mail-bw0-f227.google.com ([209.85.218.227]:61495 "EHLO mail-bw0-f227.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756787AbZLITox convert rfc822-to-8bit (ORCPT ); Wed, 9 Dec 2009 14:44:53 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=to:cc:subject:from:date:mime-version:content-disposition:message-id :content-type:content-transfer-encoding; b=dn6x0Ag9b9ytIKO8HcE/4/ZD6M2C2mv24XyTS3UKv5xXDZCOIwO0C9DRigetgwuR88 eIDOPyzcCNGZJeS7Iu1W/CQvBwp3zzFo02D5cUtYa5z2tnhZNzqkpSIYgQYO+cE024ym wffTQO0ENWyDxQUDGXNjzuzPRQtwzxbt5zOsQ= To: Jens Axboe Cc: Jeff Moyer , "Linux-Kernel" , Vivek Goyal Subject: Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed From: Corrado Zoccolo Date: Wed, 9 Dec 2009 20:45:16 +0100 MIME-Version: 1.0 Content-Disposition: inline Message-Id: <4b1ffe39.0f1abc0a.19c7.05d2@mx.google.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2115 Lines: 50 On Wed, Dec 9, 2009 at 8:05 PM, Jens Axboe wrote: > On Wed, Dec 09 2009, Jeff Moyer wrote: >> OK. Can we put a comment in there and change the initialization to >> cfq_slice_sync * 10? > > Agree, that would be MUCH easier to understand. > Sure, we can put a comment there, but I don't like hardcoding a constant that depends on how the formula is computed (what if the formula is changed, and it doesn't depend on cfq_slice_sync any more, or if cfq_slice_sync changes dynamically?). When I wrote it, what I really meant was exactly what you read in the C code (assume the last delayed sync happened 1 second ago). Then, the effect would be to start with a queue depth of 10 with the current formula, but even if we change the formula, 1 second is still meaningful (while 10 *cfq_slice_sync, that has the same value, becomes misleading). So my proposed fix is just: >From f06cd83b45b3a7ee13ae7322197b610085dc70dd Mon Sep 17 00:00:00 2001 From: Corrado Zoccolo Date: Wed, 9 Dec 2009 20:40:16 +0100 Subject: [PATCH] cfq-iosched: commenting non-obvious initialization Added a comment to explain the initialization of last_delayed_sync. Signed-off-by: Corrado Zoccolo --- block/cfq-iosched.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 98b15b9..69ecee7 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -3759,6 +3759,10 @@ static void *cfq_init_queue(struct request_queue *q) cfqd->cfq_latency = 1; cfqd->cfq_group_isolation = 0; cfqd->hw_tag = -1; + /* + * we optimistically start assuming sync ops weren't delayed in last + * second, in order to have larger depth for async operations. + */ cfqd->last_delayed_sync = jiffies - HZ; INIT_RCU_HEAD(&cfqd->rcu); return cfqd; -- 1.6.2.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/