Messages in this thread | | | Date | Fri, 18 Mar 2005 19:46:33 +1100 | From | Nick Piggin <> | Subject | Re: 2.6.11 vs 2.6.10 slowdown on i686 |
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Kurt Garloff wrote: > Hi Nick, >
Hi Kurt!
> On Thu, Mar 17, 2005 at 11:37:24PM +1100, Nick Piggin wrote: > >>Ian Pratt wrote: >> >>>fork: 166 -> 235 (40% slowdown) >>>exec: 857 -> 1003 (17% slowdown) >>> >>>I'm guessing this is down to the 4 level pagetables. This is rather a >>>surprise as I thought the compiler would optimise most of these >>>changes away. Apparently not. >> >>There are some changes in the current -bk tree (which are a >>bit in-flux at the moment) which introduce some optimisations. >> >>They should bring 2-level performance close to par with 2.6.10. >>If not, complain again :) > > > Is there a clean patchset that we should look at to test? >
Probably the best thing would be to wait and see what happens with the ptwalk patches. There is a fix in there for ia64 now, but I think that may be a temporary one.
Andi is probably keeping an eye on that, but if not then I could put a patchset together when things finalise in 2.6.
From the profiles I have seen, the ptwalk patches bring page table walking performance pretty well back to 2.6.10 levels, however the "aggressive page table freeing" (clear_page_range) changes that went in at the same time as the 4level stuff seem to be what is slowing down exit() and unmapping performance.
Not by a huge amount, mind you, and it is not completely wasted performance, because it provides better page table freeing. But it is enough to be annoying! I haven't had much time to look at it lately, but I hope to get onto it soon.
Nick
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