Re: [patch] 'multimedia latency patch', lowlatency-2.2.10-M6

Linus Torvalds (torvalds@transmeta.com)
Sat, 31 Jul 1999 13:10:11 -0700 (PDT)


On Sat, 31 Jul 1999, Ingo Molnar wrote:
> On Sat, 31 Jul 1999, Benno Senoner wrote:
>
> > as Roger Larrson suspected, there are some parts in the kernel
> > which have a too long execution path:
> > On his PPro with 512MB RAM, d_lookup takes up to 80ms to execute !
>
> yes. I've attached a patch that is supposed to make things much better.

No. Check the numbers first, d_lookup() doesn't do anything heavy (it just
follows a linked list of entries - even assuming a lot of cache misses
that would probably imply more dentries than you can fit in 512MB).

Basically, if d_lookup() takes 80ms, there's a bug somewhere. Don't try to
paper it over by adding "reschedule" calls.

The bug may be a completely buggered hash function or similar.

Or the bug may be the latency measurement.

In either case, trying to add band-aid over it is the wrong solution.

Linus

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