Re: [patch] e1000 TSO parameter

David S. Miller
2003-07-16T06:26:17Z

On Tue, 15 Jul 2003 23:32:48 -0700
David Mosberger <davidm@napali.hpl.hp.com> wrote:

> DaveM> No, I mean "bypass L2 cache on miss" for stores. Don't tell
> DaveM> me IA64 doesn't have that? 8) I certainly didn't mean "always
> DaveM> bypass L2 cache" for stores :-)
>
> What I'm saying is that I almost always want copy_user() to put the
> destination data in the cache, even if it isn't cached yet.

No you don't :-)

If you miss, you do a bypass to main memory. Then when the
app asks for the data (if it even does at all, consider that)
it get's a clean copy in it's L2 cache.

Overall it's more efficient this way.

> Many copy_user() calls are for for data structures that
> easily fit in the cache and the data is usually used quickly afterwards.

Absolutely correct. We can't use the cache bypass-on-miss stores on
sparc64 unless the copy is at least a couple of cachelines in size.

It all works out, don't worry :-)