Messages in this thread | | | Date | Wed, 18 Jan 2012 08:04:25 -0500 | From | Vivek Goyal <> | Subject | Re: [RFC 0/3]block: An IOPS based ioscheduler |
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On Wed, Jan 18, 2012 at 09:20:37AM +0800, Shaohua Li wrote:
[..] > > I think trying to make to make CFQ work (Or trying to come up with CFQ > > like IOPS scheduler) on these fast devices might not lead us anywhere. > If only performance matters, I'd rather use noop for ssd. There is > requirement to have cgroup support (maybe ioprio) to give different > tasks different bandwidth.
Sure but the issue is that we need to idle in an effort to prioritize a task and idling kills performance. So you can implement something but I have doubts that on a fast hardware it is going to be very useful.
Another issue is that with flash based storage, it can drive really deep queue depths. If that's the case, then just ioscheduler can't solve the prioritazaion issues (until and unless ioscheduler does not drive deep queue depths and kills performance). We need some kind of cooperation from device (like device understanding the notion of iopriority), so that device can prioritize the requests and one need not to idle. That way, we might be able to get service differentiation while getting reasonable throughput.
Thanks Vivek
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