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Message-ID: <564A58A3.6020005@kernel.dk> Date: Mon, 16 Nov 2015 15:28:51 -0700 From: Jens Axboe <axboe@...nel.dk> To: Jan Kara <jack@...e.com> Cc: Jeff Moyer <jmoyer@...hat.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] blk-flush: Queue through IO scheduler when flush not required On 11/12/2015 06:25 AM, Jan Kara wrote: > Currently blk_insert_flush() just adds flush request to q->queue_head > when flush is not required. That completely bypasses IO scheduler so > e.g. CFQ can be idling waiting for new request to arrive and will idle > through the whole window unnecessarily. Luckily this only happens in > rare cases as usually checks in generic_make_request_checks() clear > FLUSH and FUA flags early if they are not needed. > > When no flushing is actually required, we can easily fix the problem by > properly queueing the request through the IO scheduler. Ideally IO > scheduler should be also made aware of requests queued via > blk_flush_queue_rq(). However inserting flush request through IO > scheduler can have unwanted side-effects since due to flush batching > delaying the flush request in IO scheduler will delay all flush requests > possibly coming from other processes. So we keep adding the request > directly to q->queue_head. Applied, thanks Jan. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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