Re: [RFC] x86-64: Use SSE for copy_page and clear_page

[Denis Vlasenko <vda@ilport.com.ua>]

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On Wednesday 01 June 2005 09:22, Denis Vlasenko wrote:
> On Tuesday 31 May 2005 16:59, Benjamin LaHaise wrote:
> > On Tue, May 31, 2005 at 11:23:58AM +0200, Andi Kleen wrote:
> > > fork is only a corner case. The main case is a process allocating
> > > memory using brk/mmap and then using it.
> 
> I did the tests. I confirm Andi's conclusion that
> if you are going to use cleared/copied page immediately,
> nt stores are a loss.

For anyone interested, here are the results and tarball with patch
which allows to switch routines on the fly, plus test programs/scripts.

You need to apply the patch, compile programs (see testing/mk)
and run (see testing/m).

Zero 1 page (4k), x300000 times:
./zero1 4 300000
method............. times.................. clears/copies
slow:               0m2.094 0m2.143 0m2.143 1800225/332
mmx_APn:            0m1.931 0m2.036 0m2.053 1800207/316
mmx_APN:            0m3.458 0m3.476 0m3.487 1800212/335
mmx_APn/APN:        0m2.023 0m2.057 0m2.225 1800205/297
n - normal stores, N - nt stores, n/N - nt stores for copy only

Zero 100 pages, x3000 times (zero all pages, read back all pages):
./zero1 400 3000
slow:               0m2.861 0m2.865 0m2.958 909218/323
mmx_APn:            0m2.626 0m2.715 0m2.783 909208/307
mmx_APN:            0m2.240 0m2.249 0m2.251 909212/294
mmx_APn/APN:        0m2.715 0m2.752 0m2.761 909220/324

Zero 100 pages, x3000 times (zero page, read back page, repeat for all pages):
./zero2 400 3000
slow:               0m1.711 0m1.734 0m1.739 909211/306
mmx_APn:            0m1.548 0m1.585 0m1.616 909208/303
mmx_APN:            0m2.088 0m2.102 0m2.104 909203/287
mmx_APn/APN:        0m1.589 0m1.603 0m1.617 909202/288

Andi is right. If we read pages back immediately, we lose.
If we defer that, we win.

Fork and copy 1 page, x150000 times
./copy1 4 150000
slow:               0m4.464 0m4.487 0m4.495 1350240/900353
mmx_APn:            0m3.979 0m4.090 0m4.191 1350229/900327
mmx_APN:            0m5.685 0m5.722 0m5.744 1350229/900348
mmx_APn/APN:        0m4.730 0m4.826 0m4.975 1350221/900340

Fork and copy 100 pages, x1500 times (copy all pages, read back all copied pages):
./copy1 400 1500
slow:               0m2.561 0m2.568 0m2.576 14019/454824
mmx_APn:            0m2.230 0m2.237 0m2.242 14011/454804
mmx_APN:            0m1.841 0m1.865 0m1.876 14008/454791
mmx_APn/APN:        0m1.906 0m1.909 0m1.922 14010/454788

Fork and copy 100 pages, x1500 times (copy page, read back copied page, repeat for each page):
./copy2 400 1500
slow:               0m2.097 0m2.107 0m2.121 14020/454821
mmx_APn:            0m1.769 0m1.776 0m1.788 14008/454787
mmx_APN:            0m1.975 0m1.978 0m2.015 14035/454791
mmx_APn/APN:        0m1.979 0m2.009 0m2.017 14013/454810
--
vda

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