Re: [PATCH] livelock in elevator scheduling

[kumon@flab.fujitsu.co.jp]

Jens Axboe writes:
 > > Problem:
 > >  Current elevator_linus() traverses the I/O requesting queue from the
 > > tail to top. And when the current request has smaller sector number
 > > than the request on the top of queue, it is always placed just after
 > > the top.
 > >  This means, if requests in some sector range are continuously
 > > generated, a request with larger sector number is always places at the
 > > last and has no chance to go to the front.  e.g. it is not scheduled.
 > 
 > 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.

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.

Anyway, I'll try your patch.

--
Computer Systems Laboratory, Fujitsu Labs.
kumon@flab.fujitsu.co.jp
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