Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753105AbZKGVhC (ORCPT ); Sat, 7 Nov 2009 16:37:02 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751702AbZKGVhA (ORCPT ); Sat, 7 Nov 2009 16:37:00 -0500 Received: from fg-out-1718.google.com ([72.14.220.156]:38249 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751580AbZKGVg7 (ORCPT ); Sat, 7 Nov 2009 16:36:59 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=from:to:subject:date:user-agent:mime-version:content-type :content-transfer-encoding:content-disposition:message-id; b=xmf4ESCaMbxPNIy2wSYVTa7mjvIIST+Zo8xsSVfsupEFmA4puHkVdM8W/PA+EXkiTy gYueX5BsdIBnF+MfjdfLw2cQTWUgkeyKcIqY5ULmCS8rM51JXG8EwHvEcJIH7ttXBLNI 0kaUcbM4wgrD5HI73C2Vze3AjtigT/sufYAb0= From: Corrado Zoccolo To: "Linux-Kernel" , Jens Axboe , Jeff Moyer Subject: [PATCH] cfq-iosched: fix next_rq computation Date: Sat, 7 Nov 2009 22:37:01 +0100 User-Agent: KMail/1.11.4 (Linux/2.6.32cz; KDE/4.2.4; i686; ; ) MIME-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200911072237.01807.czoccolo@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4063 Lines: 103 Cfq has a bug in computation of next_rq, that affects transition between multiple sequential request streams in a single queue (e.g.: two sequential buffered writers of the same priority), causing the alternation between the two streams for a transient period. 8,0 1 18737 0.260400660 5312 D W 141653311 + 256 8,0 1 20839 0.273239461 5400 D W 141653567 + 256 8,0 1 20841 0.276343885 5394 D W 142803919 + 256 8,0 1 20843 0.279490878 5394 D W 141668927 + 256 8,0 1 20845 0.292459993 5400 D W 142804175 + 256 8,0 1 20847 0.295537247 5400 D W 141668671 + 256 8,0 1 20849 0.298656337 5400 D W 142804431 + 256 8,0 1 20851 0.311481148 5394 D W 141668415 + 256 8,0 1 20853 0.314421305 5394 D W 142804687 + 256 8,0 1 20855 0.318960112 5400 D W 142804943 + 256 The fix makes sure that the next_rq is computed from the last dispatched request, and not affected by merging. 8,0 1 37776 4.305161306 0 D W 141738087 + 256 8,0 1 37778 4.308298091 0 D W 141738343 + 256 8,0 1 37780 4.312885190 0 D W 141738599 + 256 8,0 1 37782 4.315933291 0 D W 141738855 + 256 8,0 1 37784 4.319064459 0 D W 141739111 + 256 8,0 1 37786 4.331918431 5672 D W 142803007 + 256 8,0 1 37788 4.334930332 5672 D W 142803263 + 256 8,0 1 37790 4.337902723 5672 D W 142803519 + 256 8,0 1 37792 4.342359774 5672 D W 142803775 + 256 8,0 1 37794 4.345318286 0 D W 142804031 + 256 --- block/cfq-iosched.c | 13 +++++++------ 1 files changed, 7 insertions(+), 6 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 56cfd1b..f5a1de7 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -454,9 +454,9 @@ static inline bool cfq_slice_used(struct cfq_queue *cfqq) * behind the head is penalized and only allowed to a certain extent. */ static struct request * -cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2) +cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2, sector_t last) { - sector_t last, s1, s2, d1 = 0, d2 = 0; + sector_t s1, s2, d1 = 0, d2 = 0; unsigned long back_max; #define CFQ_RQ1_WRAP 0x01 /* request 1 wraps */ #define CFQ_RQ2_WRAP 0x02 /* request 2 wraps */ @@ -479,8 +479,6 @@ cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2) s1 = blk_rq_pos(rq1); s2 = blk_rq_pos(rq2); - last = cfqd->last_position; - /* * by definition, 1KiB is 2 sectors */ @@ -595,7 +593,7 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq, next = rb_entry_rq(rbnext); } - return cfq_choose_req(cfqd, next, prev); + return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last)); } static unsigned long cfq_slice_offset(struct cfq_data *cfqd, @@ -843,7 +841,7 @@ static void cfq_add_rq_rb(struct request *rq) * check if this request is a better next-serve candidate */ prev = cfqq->next_rq; - cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq); + cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position); /* * adjust priority tree position, if ->next_rq changes @@ -950,6 +948,7 @@ static void cfq_merged_requests(struct request_queue *q, struct request *rq, struct request *next) { + struct cfq_queue *cfqq = RQ_CFQQ(rq); /* * reposition in fifo if next is older than rq */ @@ -959,6 +958,8 @@ cfq_merged_requests(struct request_queue *q, struct request *rq, rq_set_fifo_time(rq, rq_fifo_time(next)); } + if (cfqq->next_rq == next) + cfqq->next_rq = rq; cfq_remove_request(next); } -- 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/