Messages in this thread | | | Date | Thu, 17 Mar 2005 23:37:24 +1100 | From | Nick Piggin <> | Subject | Re: 2.6.11 vs 2.6.10 slowdown on i686 |
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Ian Pratt wrote: > Folks, > > When we upgraded arch xen/x86 to kernel 2.6.11, we noticed a slowdown > on a number of micro-benchmarks. In order to investigate, I built > native (non Xen) i686 uniprocessor kernels for 2.6.10 and 2.6.11 with > the same configuration and ran lmbench-3.0-a3 on them. The test > machine was a 2.4GHz Xeon box, gcc 3.3.3 (FC3 default) was used to > compile the kernels, NOHIGHMEM=y (2-level only). > > On the i686 fork and exec benchmarks I found that there's been a > significant slowdown between 2.6.10 and 2.6.11. Some of the other > numbers a bit ugly too (see attached). > > 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 :)
Thanks, Nick
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