Peter Wemm peter at
Fri Mar 28 16:23:25 PST 2003

Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= wrote:
> David Malone <dwmalone at> writes:
> > On Thu, Mar 27, 2003 at 09:57:35AM +0100, des at wrote:
> > > Might it be a good idea to have separate b{copy,zero} implementations
> > > for special purposes like pmap_{copy,zero}_page?
> > We do have a i686_pagezero already, which seems to be used in
> > pmap_zero_page - I guess it may not be well tuned to modern processors,
> > as it is almost 5 years old.
> i686_pagezero uses 'rep stosl' after an initial 'rep scasl' to check
> if the page was already zero (which is a pessimization unless we zero
> a lot of pages that are already zeroed).  SSE can do far better than
> that.

i686_pagezero was written with SMP in mind.  The cache state ends up in
a more favourable condition when sharing with other cpus.

Peter Wemm - peter at; peter at; peter at
"All of this is for nothing if we don't go to the stars" - JMS/B5

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