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Date: Tue, 21 Nov 2000 12:36:08 +0100
From: Jens Axboe <axboe@suse.de>
To: kumon@flab.fujitsu.co.jp
Cc: linux-kernel@vger.kernel.org, Dave Jones <davej@suse.de>,
        Andrea Arcangeli <andrea@suse.de>
Subject: Re: [PATCH] livelock in elevator scheduling
Message-ID: <20001121123608.F10007@suse.de>
In-Reply-To: <200011210838.RAA27382@asami.proc.flab.fujitsu.co.jp> <20001121112836.B10007@suse.de> <200011211130.UAA27961@asami.proc.flab.fujitsu.co.jp>
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In-Reply-To: <200011211130.UAA27961@asami.proc.flab.fujitsu.co.jp>; from kumon@flab.fujitsu.co.jp on Tue, Nov 21, 2000 at 08:30:33PM +0900
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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
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