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SubjectRe: [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space
On 05/04/2010 03:56 PM, Takuya Yoshikawa wrote:
> [Performance test]
>
> We measured the tsc needed to the ioctl()s for getting dirty logs in
> kernel.
>
> Test environment
>
> AMD Phenom(tm) 9850 Quad-Core Processor with 8GB memory
>
>
> 1. GUI test (running Ubuntu guest in graphical mode)
>
> sudo qemu-system-x86_64 -hda dirtylog_test.img -boot c -m 4192 -net ...
>
> We show a relatively stable part to compare how much time is needed
> for the basic parts of dirty log ioctl.
>
> get.org get.opt switch.opt
>
> slots[7].len=32768 278379 66398 64024
> slots[8].len=32768 181246 270 160
> slots[7].len=32768 263961 64673 64494
> slots[8].len=32768 181655 265 160
> slots[7].len=32768 263736 64701 64610
> slots[8].len=32768 182785 267 160
> slots[7].len=32768 260925 65360 65042
> slots[8].len=32768 182579 264 160
> slots[7].len=32768 267823 65915 65682
> slots[8].len=32768 186350 271 160
>
> At a glance, we know our optimization improved significantly compared
> to the original get dirty log ioctl. This is true for both get.opt and
> switch.opt. This has a really big impact for the personal KVM users who
> drive KVM in GUI mode on their usual PCs.
>
> Next, we notice that switch.opt improved a hundred nano seconds or so for
> these slots. Although this may sound a bit tiny improvement, we can feel
> this as a difference of GUI's responses like mouse reactions.
>

100 ns... this is a bit on the low side (and if you can measure it
interactively you have much better reflexes than I).

> To feel the difference, please try GUI on your PC with our patch series!
>

No doubt get.org -> get.opt is measurable, but get.opt->switch.opt is
problematic. Have you tried profiling to see where the time is spent
(well I can guess, clearing the write access from the sptes).

>
> 2. Live-migration test (4GB guest, write loop with 1GB buf)
>
> We also did a live-migration test.
>
> get.org get.opt switch.opt
>
> slots[0].len=655360 797383 261144 222181
> slots[1].len=3757047808 2186721 1965244 1842824
> slots[2].len=637534208 1433562 1012723 1031213
> slots[3].len=131072 216858 331 331
> slots[4].len=131072 121635 225 164
> slots[5].len=131072 120863 356 164
> slots[6].len=16777216 121746 1133 156
> slots[7].len=32768 120415 230 278
> slots[8].len=32768 120368 216 149
> slots[0].len=655360 806497 194710 223582
> slots[1].len=3757047808 2142922 1878025 1895369
> slots[2].len=637534208 1386512 1021309 1000345
> slots[3].len=131072 221118 459 296
> slots[4].len=131072 121516 272 166
> slots[5].len=131072 122652 244 173
> slots[6].len=16777216 123226 99185 149
> slots[7].len=32768 121803 457 505
> slots[8].len=32768 121586 216 155
> slots[0].len=655360 766113 211317 213179
> slots[1].len=3757047808 2155662 1974790 1842361
> slots[2].len=637534208 1481411 1020004 1031352
> slots[3].len=131072 223100 351 295
> slots[4].len=131072 122982 436 164
> slots[5].len=131072 122100 300 503
> slots[6].len=16777216 123653 779 151
> slots[7].len=32768 122617 284 157
> slots[8].len=32768 122737 253 149
>
> For slots other than 0,1,2 we can see the similar improvement.
>
> Considering the fact that switch.opt does not depend on the bitmap length
> except for kvm_mmu_slot_remove_write_access(), this is the cause of some
> usec to msec time consumption: there might be some context switches.
>
> But note that this was done with the workload which dirtied the memory
> endlessly during the live-migration.
>
> In usual workload, the number of dirty pages varies a lot for each iteration
> and we should gain really a lot for relatively clean cases.
>

Can you post such a test, for an idle large guest?

--
error compiling committee.c: too many arguments to function



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