Messages in this thread | | | Subject | Re: [RFC] Block IO Controller V2 - some results | From | "Alan D. Brunelle" <> | Date | Tue, 17 Nov 2009 07:38:47 -0500 |
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On Mon, 2009-11-16 at 17:18 -0500, Vivek Goyal wrote: > On Mon, Nov 16, 2009 at 03:51:00PM -0500, Alan D. Brunelle wrote: > > [..] > > :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: > > > > The next thing to look at is to see what the "penalty" is for the > > additional code: see how much bandwidth we lose for the capability > > added. Here we see the sum of the system's throughput for the various > > tests: > > > > ---- ---- - ----------- ----------- ----------- ----------- > > Mode RdWr N base ioc off ioc no idle ioc idle > > ---- ---- - ----------- ----------- ----------- ----------- > > rnd rd 2 17.3 17.1 9.4 9.1 > > rnd rd 4 27.1 27.1 8.1 8.2 > > rnd rd 8 37.1 37.1 6.8 7.1 > > > > Hi Alan, > > This seems to be the most notable result in terms of performance degradation. > > I ran two random readers on a locally attached SATA disk. There in fact > I gain in terms of performance because we perform less number of seeks > now as we allocate a continous slice to one group and then move onto > next group. > > But in your setup it looks like there is a striped set of disks and seek > cost is less and waiting per group for sync-noidle workload is hurting > instead.
That is correct - there are 4 back-end buses on an MSA1000, and each LUN that is exported is constructed from 1 drive from each bus (hardware striped RAID). [There is _no_ SW RAID involved.]
> > One simple way to test that would be to set slice_idle=0 so that CFQ does > not try to do any idling at all. Can you please re-run above test. This > will help in figuring out whether above performance regression is coming > from idling on sync-noidle workload group per cgroup or not.
I'll put that in the queue - first I'm going to re-run w/ synchronous direct I/O for the writes. I'm also going to pair this down to just doing 2-processes per disk runs (to simplify results & speed up tests). Once we get that working better, I can expand things back out.
> > Above numbers are in what units?
These are in MiB/second (derived from the FIO output).
> > Thanks > Vivek
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