Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 4 Jul 2003 17:01:54 -0300 (BRT) | From | Marcelo Tosatti <> | Subject | Re: Status of the IO scheduler fixes for 2.4 |
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On Wed, 2 Jul 2003, Chris Mason wrote:
> On Wed, 2003-07-02 at 18:28, Marcelo Tosatti wrote: > > On Wed, 2 Jul 2003, Marcelo Tosatti wrote: > > > > > > > > Hello people, > > > > > > What is the status of the IO scheduler fixes for increased fairness for > > > 2.4 ? > > > > > > I haven't had time to read and think about everything you guys discussed, > > > so a brief summary would be very helpful for me. > > > > > > Danke > > > > Ah, we all want that the fairness issues to be fixed in 2.4.22, right ? > > My current code is attached, it's basically a merge of these 3 patches, > with modifications based on benchmarks and latency measurements here. > > fix_pausing: From Andrea, it fixes a few corner case races where > wakeups can be missed in wait_on_buffer, wait_on_page, and > __get_request_wait. > > elevator-low-latency: From Andrea, it keeps the amount of io on a given > queue to a reasonable number. This prevents a small number of huge > requests from introducing large latencies on smaller requests. > > q->full: From Nick, it reduces latency in __get_request_wait by making > sure new io can't come in and steal requests before old waiters are > served. > > Those represent the big 3 areas I believe the latencies are coming > from. The q->full patch can hurt throughput badly as the number of > writers increases (50% of what 2.4.21 gets for 10 or more concurrent > streaming writers), but it really seems to help desktop workloads here.
Chris,
Would you please separate those tree fixes in separate diffs?
For me it seems low latency and fix-pausing patches should be enough for "better" IO fairness. I might be wrong about that, though.
Lets try this: Include elevator-low-latency in -pre3 (which I'm trying to release today), then fix pausing in -pre4. If the IO fairness still doesnt get somewhat better for general use (well get isolated user reports and benchmarks for both the two patches), then I might consider the q->full patch (it has throughtput drawbacks and I prefer avoiding a tunable there).
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