Messages in this thread |  | | | Date | Sat, 24 Jun 2006 12:21:36 -0700 (PDT) | | From | Linus Torvalds <> | | Subject | Re: [PATCH] x86: cache pollution aware __copy_from_user_ll() |
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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 valid.
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