[lkml]   [2006]   [Jun]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] x86: cache pollution aware __copy_from_user_ll()

On Sat, 24 Jun 2006, Arjan van de Ven wrote:
> while this patch will reduce the number of cycles spent in the kernel,
> it's just pushing the cache miss to userspace (by virtue of doing a
> cache flush effectively)... is this really the right thing? The total
> memory bandwidth will actually increase with this patch if you're
> unlucky (eg if userspace decides to write to this memory eventually)....

No. It's for copying _from_ user space, ie a "write()" system call. So
what it does is to effectively try to use non-temporal stores to the page
cache - since the page cache is usually not read directly afterwards (at
least not soon enough for L1 caches to help).

I don't generally like cache tricks either (caches tend to be better than
humans, or at least get there fairly soon), but this one does seem very

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2009-11-18 23:46    [W:0.054 / U:19.128 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site