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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

> > > 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 :
> > > http://pastebin.com/raw.php?i=Dy71Fegq
> > > 
> > > 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

Startup.
> > 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

Perhaps?
> 
> 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.

> 
> Greetings
> Tobias

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