Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752065AbbFYXfq (ORCPT ); Thu, 25 Jun 2015 19:35:46 -0400 Received: from mail-vn0-f45.google.com ([209.85.216.45]:44121 "EHLO mail-vn0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751421AbbFYXf1 (ORCPT ); Thu, 25 Jun 2015 19:35:27 -0400 MIME-Version: 1.0 In-Reply-To: <20150625234030.4dc99725@tom-T450> References: <1434894751-6877-1-git-send-email-akinobu.mita@gmail.com> <1434894751-6877-4-git-send-email-akinobu.mita@gmail.com> <20150625234030.4dc99725@tom-T450> Date: Fri, 26 Jun 2015 08:35:26 +0900 Message-ID: Subject: Re: [PATCH 3/4] blk-mq: establish new mapping before cpu starts handling requests From: Akinobu Mita To: Ming Lei Cc: Linux Kernel Mailing List , Jens Axboe Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3622 Lines: 97 2015-06-26 0:40 GMT+09:00 Ming Lei : > On Thu, 25 Jun 2015 21:49:43 +0900 > Akinobu Mita wrote: >> For example, there is a single hw queue (hctx) and two CPU queues >> (ctx0 for CPU0, and ctx1 for CPU1). Now CPU1 is just onlined and >> a request is inserted into ctx1->rq_list and set bit0 in pending >> bitmap as ctx1->index_hw is still zero. >> >> And then while running hw queue, flush_busy_ctxs() finds bit0 is set >> in pending bitmap and tries to retrieve requests in >> hctx->ctxs[0].rq_list. But htx->ctxs[0] is ctx0, so the request in >> ctx1->rq_list is ignored. > > Per current design, the request should have been inserted into ctx0 instead > of ctx1 because ctx1 isn't mapped yet even though ctx1->cpu becomes ONLINE. > > So how about the following patch? which looks much simpler. OK, I'll try this patch to see if the problem disappears. > --- > diff --git a/block/blk-mq.c b/block/blk-mq.c > index f537796..2f45b73 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1034,7 +1034,12 @@ void blk_mq_insert_request(struct request *rq, bool at_head, bool run_queue, > struct blk_mq_ctx *ctx = rq->mq_ctx, *current_ctx; > > current_ctx = blk_mq_get_ctx(q); > - if (!cpu_online(ctx->cpu)) > + /* > + * ctx->cpu may become ONLINE but ctx hasn't been mapped to > + * hctx yet because there is a tiny race window between > + * ctx->cpu ONLINE and doing the remap > + */ > + if (!blk_mq_ctx_mapped(ctx)) > rq->mq_ctx = ctx = current_ctx; > > hctx = q->mq_ops->map_queue(q, ctx->cpu); > @@ -1063,7 +1068,7 @@ static void blk_mq_insert_requests(struct request_queue *q, > > current_ctx = blk_mq_get_ctx(q); > > - if (!cpu_online(ctx->cpu)) > + if (!blk_mq_ctx_mapped(ctx)) > ctx = current_ctx; > hctx = q->mq_ops->map_queue(q, ctx->cpu); > > @@ -1816,13 +1821,16 @@ static void blk_mq_map_swqueue(struct request_queue *q) > */ > queue_for_each_ctx(q, ctx, i) { > /* If the cpu isn't online, the cpu is mapped to first hctx */ > - if (!cpu_online(i)) > + if (!cpu_online(i)) { > + ctx->mapped = 0; > continue; > + } > > hctx = q->mq_ops->map_queue(q, i); > cpumask_set_cpu(i, hctx->cpumask); > cpumask_set_cpu(i, hctx->tags->cpumask); > ctx->index_hw = hctx->nr_ctx; > + ctx->mapped = 1; > hctx->ctxs[hctx->nr_ctx++] = ctx; > } > > diff --git a/block/blk-mq.h b/block/blk-mq.h > index 6a48c4c..52819ad 100644 > --- a/block/blk-mq.h > +++ b/block/blk-mq.h > @@ -10,7 +10,8 @@ struct blk_mq_ctx { > } ____cacheline_aligned_in_smp; > > unsigned int cpu; > - unsigned int index_hw; > + unsigned int index_hw : 16; > + unsigned int mapped : 1; > > unsigned int last_tag ____cacheline_aligned_in_smp; > > @@ -123,4 +124,9 @@ static inline bool blk_mq_hw_queue_mapped(struct blk_mq_hw_ctx *hctx) > return hctx->nr_ctx && hctx->tags; > } > > +static inline bool blk_mq_ctx_mapped(struct blk_mq_ctx *ctx) > +{ > + return ctx->mapped; > +} > + > #endif > > -- 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/