Messages in this thread | | | Date | Fri, 10 Jun 2011 05:29:22 -0400 | From | Vivek Goyal <> | Subject | Re: CFQ: async queue blocks the whole system |
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On Fri, Jun 10, 2011 at 11:20:43AM +0200, Jens Axboe wrote: > On 2011-06-10 11:17, Vivek Goyal wrote: > > On Fri, Jun 10, 2011 at 09:19:12AM +0800, Shaohua Li wrote: > > > > [..] > >>> If there is no major advantage of draining sync requests before async > >>> is dispatched, I think this should be an easy fix. > >> I thought this is to avoid sync latency if we switch from an async > >> queue to sync queue later. > > > > Is it about the sync request latency which has already been dispatched? I > > really wish that driver and disk should do some prioritazation for reads > > here and CFQ does not have to jump through hoops like drain sync requests > > before async requests are dispatched. > > That would never work. Are you suggesting putting that logic in all > drivers? Or relying on hardware to get the fairness right? Not going to > happen.
I was hoping that hardware does some prioritization. Well, in this case even if hardware maintains FIFO behavior it should be good enough.
But I would not claim anything in this regard as I have never experimented with it and have no idea that how sync latencies are impacted if we don't drain the queue before dispathing WRITEs.
I was just wondering that with current generation hardware is it bad enough that we need to keep this logic around?
Thanks Vivek
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