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SubjectRe: Terrible elevator performance in kernel 2.4.0-test8
On Thu, Sep 14, 2000 at 07:40:12PM +1000, Robert Cohen wrote:

> What I believe is happening is that the elevator isn't merging the
> requests properly.
> I think that this may be the same problem reported here
> http://www.uwsg.indiana.edu/hypermail/linux/kernel/0008.2/0389.html

The merging issue pointed out by Giuliano Pochini is there since 2.2.0.

> With kernel version 2.4.0-test1-ac22, I saw adequate performance.

In 2.4.0-test1-ac22 there were a latency-driven elevator (the one we have
now since test2 can't provide good latency anymore).

So if something it should be the other way around, the elevator that we
have since test2 should provide _better_ throghput and _less_ seeks. Thus
it can't be the elevator algorithm but maybe as Ingo said something in the
plugging that broke during the test2 changes.

> In 2.4.0-test3 - test6, the default max_bombs value became 0. And the
> performance with this setting was terrible.

It's zero because in reality is not limited anymore, this just mean it
should provide better performance and worse latency.

> Although I still saw a tendency for a client to get write starved.

Are you doing synchronous writes, right?

> Unfortunately, the benchmarks don't show any improvement.

tiotest should provide better numbers with the elevator from test2
(compared to the test1 one).

Andrea
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