Re: [PATCH] livelock in elevator scheduling

Jens Axboe
2000-11-21T12:06:29Z

On Tue, Nov 21 2000, kumon@flab.fujitsu.co.jp wrote:
> > Believe it or not, but this is intentional. In that regard, the
> > function name is a misnomer -- call it i/o scheduler instead :-)
>
> I never believe it intentional. If it is true, the current kernel
> will be suffered from a kind of DOS attack. Yes, actually I'm a
> victim of it.

The problem is caused by the too high sequence numbers in stock
kernel, as I said. Plus, the sequence decrementing doesn't take
request/buffer size into account. So the starvation _is_ limited,
the limit is just too high.

> By Running ZD's ServerBench, not only the performance down, but my
> machine blocks all commands execution including /bin/ps, /bin/ls... ,
> and those are not ^C able unless the benchmark is stopped. Those
> commands are read from disks but the requests are wating at the end of
> I/O queue, those won't be executed.

If performance is down, then that problem is most likely elsewhere.
I/O limited benchmarking typically thrives on lots of request
latency -- with that comes better throughput for individual threads.

> Anyway, I'll try your patch.

Thanks

--
* Jens Axboe <axboe@suse.de>
* SuSE Labs