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SubjectRe: CONFIG_PREEMPT and server workloads
At Thu, 18 Mar 2004 22:10:06 -0800,
Andrew Morton wrote:
>
> Takashi Iwai <tiwai@suse.de> wrote:
> >
> > BTW, i had the worst latency in sis900's timer handler.
> > it takes 3ms, and hard to fix, too :-<
>
> It's all coming back to me now.
>
> The worst-case latency is during umount, fs/inode.c:invalidate_list() when
> the filesystem has a zillion inodes in icache. Measured 250 milliseconds
> on a 256MB 2.7GHz P4 here. OK, so don't do that.

also that's not included in my test case :)

> The unavoidable worst case is in the RCU callbacks for dcache shrinkage -
> I've seen 25 millisecond holdoffs on the above machine during filesystem
> stresstests when RCU is freeing a huge number of dentries in softirq
> context.

hmm, this wasn't also evaluated in my tests.
it's worthy to try. thanks for the info.

> This if Hard To Fix. Dipankar spent quite some time looking into it and
> had patches, but I lost track of where they're at.

couldn't this tasklet be replaced with workqueue or such?


Takashi
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