Messages in this thread | | | Date | Wed, 18 Oct 2006 13:14:07 +0200 | From | Jens Axboe <> | Subject | Re: Bandwidth Allocations under CFQ I/O Scheduler |
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On Wed, Oct 18 2006, Helge Hafting wrote: > Jens Axboe wrote: > >While that may make some sense internally, the exported interface would > >never be workable like that. It needs to be simple, "give me foo kb/sec > >with max latency bar for this file", with an access pattern or assumed > >sequential io. > > > >Nobody speaks of iops/sec except some silly benchmark programs. I know > >that you are describing pseudo-iops, but it still doesn't make it more > >clear. > >Things aren't as simple > > > How about "give me 10% of total io capacity?" People understand > this, and the io scheduler can then guarantee this by ensuring > that the process gets 1 out of 10 io requests as long as it > keeps submitting enough.
The thing about disks is that it's not as easy as giving the process 10% of the io requests issued. Only if the considered bandwidth is random load will that work, but that's not very interesting.
You need to say 10% of the disk time, which is something CFQ can very easily be modified to do since it works with time slices already. 10% doesn't mean very much though, you need a timeframe for that to make sense anyways. Give me 100msec every 1000msecs makes more sense.
-- Jens Axboe
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