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Date: Tue, 13 Sep 2011 09:04:01 +0800 From: Shaohua Li <shaohua.li@...el.com> To: Tejun Heo <htejun@...il.com> Cc: lkml <linux-kernel@...r.kernel.org>, Jens Axboe <jaxboe@...ionio.com>, Vivek Goyal <vgoyal@...hat.com> Subject: Re: [RFC]block: don't mark flush request as SOFTBARRIER On Sun, 2011-09-11 at 10:51 +0800, Tejun Heo wrote: > Hello, > > On Thu, Sep 08, 2011 at 09:29:54AM +0800, Shaohua Li wrote: > > I'm wondering why flush request should be marked as > > SOFTBARRIER. Current flush sequence guarantees the correctness of > > flush even the request is reordered by ioscheduler. > > The primary reason would be because when those flush data requests are > put on the dispatch queue, it doesn't go through elv_dispatch_sort(). > SOFTBARRIERs function as dispatch sort boundaries and queueing flush > data request at the head w/o SOFTBARRIER would confuse dispatch > sorting, and we want to put it at the head of dispatch queue to > decrease latency for flush sequence. we do the flush first and then dispatch the data. The flush is already delayed a lot, so if latency is a problem, we already saw it. Why not just remove SOFTBARRIER and use elv_dispatch_sort() for flush data so drive can better arrange requests? Thanks, Shaohua -- 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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