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Re: [Xen-devel] Degregated I/O Performance since 3.4 - Regression in 3.4?

Am 24.04.2012 18:30, schrieb Konrad Rzeszutek Wilk:
I redid the test;

a) with 3.3.0 kernel
b) with 3.4.0-rc4
c) with 3.40-rc4 and above patch

everything else remained the same, i.e. test-program and test-scenario
was not changed and started after about 5min of domu bootup (so that no
strange bootup-effects become relevant); same phy-backend (lvm on ssd),
same everything else; so i cant see what else except the used dom0
kernel is causing this issue; but here are the numbers:

a) read: 135mb/s write: 142mb/s
b) read: 39mb/s  write: 39mb/s
c) read: 40mb/s  write: 40mb/s

Only thing that may become relevant is the difference in kernel-config
betwen 3.3 and 3.4 - here's the diff :

Jan, it seems you're right: The patch doesn't add extra performance
regression - i guess i had an i/o intensive task running in dom0 while
doing the benchmark yesterday, so that the write performance got so bad.
sorry for that.

Still there's a significant performance penalty from 3.3 to 3.4
Could you please try to revert the following commits?

git revert -n a71e23d9925517e609dfcb72b5874f33cdb0d2ad
No way
git revert -n 3389bb8bf76180eecaffdfa7dd5b35fa4a2ce9b5
git revert -n 4dae76705fc8f9854bb732f9944e7ff9ba7a8e9f
Hm, this is just during startup.
git revert -n b2167ba6dd89d55ced26a867fad8f0fe388fd595
No way.

git revert -n 4f14faaab4ee46a046b6baff85644be199de718c
Perhaps? But I am not seeing it.

git revert -n 9846ff10af12f9e7caac696737db6c990592a74a
after reverting said 6 commits (thanks for the ids of these - had difficulties
to find them), the performance is back to normal.

should i try to circle it down to one of this 6, or do you have a hint on
which it might be?
I think either off these: 4f14faaab4ee46a046b6baff85644be199de718c
9846ff10af12f9e7caac696737db6c990592a74a might be the culprit.

Try the 9846ff10 first.



9846ff10 was it!
after reverting it, performance returned to normal.


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