Messages in this thread | | | Date | Tue, 1 Jul 2008 08:43:26 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: follow_page() performance regressions |
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On Tue, 1 Jul 2008, Paul Mundt wrote: > > So yes, the ZERO_PAGE handling in follow_page() is causing the slow-down here.
I suspect it could be any of:
- actual code generation differences in follow_page() (some SH person needs to check that)
- some cache issue on SH. ZERO_PAGE is a single page at a fixed virtual address, while it used to populate the page tables with individual pages. Normally, this should be *better* for caching, but maybe there is some conflict? What kind of caches does SH have (virtually indexed?)
- hackbench relying on follow_page() to populate the page tables, which it no longer does for anonymous areas (using ZERO_PAGE directly instead).
Again, normally this would speed things up (fewer TLB misses etc), but if it then causes a new page fault that used to have been covered by follow_page(), who knows?
What does hackbench actually do? Anybody?
Linus
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