Re: [patch] e1000 TSO parameter

["David S. Miller" <davem@redhat.com>]

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 :-)