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SubjectRe: X15 alpha release: as fast as TUX but in user space (fwd)
Ingo Oeser writes:
> On Sun, Apr 29, 2001 at 12:48:06PM -0600, Richard Gooch wrote:
> > Ingo Oeser writes:
> > > There we have 10x faster memmove/memcpy/bzero for 1K blocks
> > > granularity (== alignment is 1K and size is multiple of 1K), that
> > > is done by the memory controller.
> > This sounds different to me. Using the memory controller is (should
> > be!) a privileged operation, thus it requires a system call. This is
> > quite different from code in a magic page, which is excuted entirely
> > in user-space. The point of the magic page is to avoid the syscall
> > overhead.
>
> Yes, but we currently have more than 10K cycles for doing
> memset of a page. If we do an syscall, we have around 600-900
> (don't know exactly), which is still less.
>
> The point is: The code in that "magic page" that considers the
> tradeoff is KERNEL code, which is designed to care about such
> trade-offs for that machine.

Um, yes. I don't disagree with that. I'm just saying the two issues
are conceptually separate, and should be considered independently.

> Glibc never knows this stuff and shouldn't, because it is already
> bloated.

True, true and true.

Regards,

Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca
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