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SubjectRe: [patch v2 0/8]block: An IOPS based ioscheduler
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On Mon, 2012-01-30 at 10:30 -0500, Vivek Goyal wrote:
> On Mon, Jan 30, 2012 at 03:02:13PM +0800, Shaohua Li wrote:
> > An IOPS based I/O scheduler
> >
> > Flash based storage has some different characteristics against rotate disk.
> > 1. no I/O seek.
> > 2. read and write I/O cost usually is much different.
> > 3. Time which a request takes depends on request size.
> > 4. High throughput and IOPS, low latency.
>
> Hi Shaohua,
>
> Last time we agreed that you will try to extend CFQ iops mode to take care
> of this case. I was wondering that if that idea is out of the window?
I felt there is complexity to do the merge and mess code even with
wrapping some functions as you suggested. Another thing is I want to
avoid complexity of CFQ, for example allocating queue and sharing it
between tasks. cfq_set_request is one source that queue_lock gets
contented, making the code simple can avoid such contention.

> Also what's the real workload where this is going to benefit us. I had
> struggled to run something which drove constantly deep queue depths to
> get the fairness without idling.
To be honest, I don't have real workload. Our test environment runs some
micro benchmarks, which has some problems. I thought we all agreed CFQ
has some limitations. Hoping somebody having real workload can have a
look.

Thanks,
Shaohua



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