Messages in this thread | | | Date | Thu, 13 Jan 2005 10:16:54 +1100 | From | Nick Piggin <> | Subject | Re: page table lock patch V15 [0/7]: overview |
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Andrew Morton wrote: > Christoph Lameter <clameter@sgi.com> wrote: > >>>Do we have measurements of the negative and/or positive impact on smaller >> >> > machines? >> >> Here is a measurement of 256M allocation on a 2 way SMP machine 2x >> PIII-500Mhz: >> >> Gb Rep Threads User System Wall flt/cpu/s fault/wsec >> 0 10 1 0.005s 0.016s 0.002s 54357.280 52261.895 >> 0 10 2 0.008s 0.019s 0.002s 43112.368 42463.566 >> >> With patch: >> >> Gb Rep Threads User System Wall flt/cpu/s fault/wsec >> 0 10 1 0.005s 0.016s 0.002s 54357.280 53439.357 >> 0 10 2 0.008s 0.018s 0.002s 44650.831 44202.412 >> >> So only a very minor improvements for old machines (this one from ~ 98). > > > OK. But have you written a test to demonstrate any performance > regressions? From, say, the use of atomic ops on ptes? >
Performance wise, Christoph's never had as much of a problem as my patches because it isn't doing extra atomic operations in copy_page_range.
However, it looks like it should be. For the same reason there needs to be an atomic read in handle_mm_fault. And it probably needs atomic ops in other places too, I think.
So my patches cost about 7% in lmbench fork benchmark... however, I've been thinking we could take the mmap_sem for writing before doing the copy_page_range which could reduce the need for atomic ops.
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