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SubjectRe: andrea buffer code (2.2.9-C.gz)
On Fri, 21 May 1999, Andrea Arcangeli wrote:

> >Indeed. In cases like these, might it make some sense to have some fixed
> >number of spinlocks and choose which to use with some reductive function?
>
> Impacting runtime performances to SMP scale better, is going to lose
> according to me. I think that if you want to SMP scale better it worth
> to pay _only_ with memory wastage and _not_ with wasted CPU cycles.

If you can be fairly sure that there won't be seriously degenerate
situations, a simple reduction (a pair of xors to reduce 32bits to
256) wastes only 1K, and surely might improve performance on 4+-way
machines?

> But as just said masp0008 raised the issue of the io_request_lock that
> is just held all the time so we can't scale better at all even using one
> spinlock per bit of memory in the machine :-). This is the only thing
> that obviously convinced me to remove the spinlock immediatly.

Yes, that makes rather a big difference :

Matthew.


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