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Message-ID: <20100301080233.GO5768@kernel.dk> Date: Mon, 1 Mar 2010 09:02:34 +0100 From: Jens Axboe <jens.axboe@...cle.com> To: Shaohua Li <shaohua.li@...el.com> Cc: linux-kernel@...r.kernel.org, czoccolo@...il.com, vgoyal@...hat.com, jmoyer@...hat.com, guijianfeng@...fujitsu.com Subject: Re: [PATCH] cfq-iosched: quantum check tweak --resend On Mon, Mar 01 2010, Shaohua Li wrote: > Currently a queue can only dispatch up to 4 requests if there are other queues. > This isn't optimal, device can handle more requests, for example, AHCI can > handle 31 requests. I can understand the limit is for fairness, but we could > do a tweak: if the queue still has a lot of slice left, sounds we could > ignore the limit. Test shows this boost my workload (two thread randread of > a SSD) from 78m/s to 100m/s. > Thanks for suggestions from Corrado and Vivek for the patch. As mentioned before, I think we definitely want to ensure that we drive the full queue depth whenever possible. I think your patch is a bit dangerous, though. The problematic workload here is a buffered write, interleaved with the occasional sync reader. If the sync reader has to endure 32 requests every time, latency rises dramatically for him. -- 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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