David Mosberger wrote:
On Thu, 24 Mar 2005 18:18:17 +1100, Nick Piggin <[EMAIL PROTECTED]> said:
Nick> After applying the recent freepgt patchset from Hugh (on
Nick> lkml), the time to fork+exit a process mapping 64GB of address
Nick> (32MB of page tables) is 0.471s. With the prefetch patch, this
Nick> drops to 0.357s.
Sorry, above numbers were wrong:
0.118s versus 0.089s. Improvement ratio is the same, I just used the
wrong divisor.
Looks like a nice improvement to me.
Does prefetching 1 line ahead give the best results? That's only
128/8=16 PTEs. Assuming a 200 cycle latency, this would allow
for only 12.5 cycles/iteration. Especially for large (NUMA) machines,
prefetching further out might help more.
Hmm... yeah it may do. Although I don't think that changes your cycles
/ iteration ratio, does it? Just allows for for a little bit more
variation.
I just retested, and prefetching 2 lines ahead gives virtually the same
performance.
But actually, my tests are set up so each pte page has only a single
'present' pte (I did it that way to speed up initial faulting time).
So the loop will almost always get stopped by the pte_none tests. So
perhaps that is able to complete in close to or less than 12 cycles.
Nick
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