Re: Serious performance degradation on a RAID with kernel 2.6.10-bk7and later

[Andreas Hirstius]

Hi,

The fls() patch from David solves the problem :-))

Do you have an idea, when it will be in the mainline kernel??

Andreas



Bartlomiej ZOLNIERKIEWICZ wrote:

> Hi!
>
> > A small update.
> >
> > Patching mm/filemap.c is not necessary in order to get the improved
> > performance!
> > It's sufficient to remove roundup_pow_of_two from  |get_init_ra_size ...
> >
> > So a simple one-liner changes to picture dramatically.
> > But why ?!?!?
>
>
> roundup_pow_of_two() uses fls() and ia64 has buggy fls() implementation
> [ seems that David fixed it but patch is not in the mainline yet]:
>
> http://www.mail-archive.com/linux-ia64@xxxxxxxxxxxxxxx/msg01196.html
>
> That would also explain why you couldn't reproduce the problem on ia32 
> Xeon machines.
>
> Bartlomiej
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