Re: mdraid write performance in different kernels up to 3.0, 3.0 shows huge improvement

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On Tue, 8 Nov 2011 10:28:57 +0100 (CET) Mikael Abrahamsson <swmike@xxxxxxxxx>
wrote:

> 
> Hello.
> 
> I have been running mdraid->cryptsetup/LUKS->lvm->xfs on Ubuntu AMD64 with 
> RAID5 and now RAID6 for quite some time, dating back to 2.6.27. Around 
> 2.6.32 I saw quite a bit of regression in write performance (probably the 
> implementation of barriers), 2.6.35 was acceptable, 2.6.38 was really 
> really bad, and 3.0 is like a rocket. Best of them all.
> 
> I'm talking about 10-20x in different in write performance on my workload, 
> in combination with the older kernels throwing me page allocation failures 
> when the write load gets high, and also quite often the machine would just 
> freeze up and had to be rebooted.
> 
> With 2.6.38 I was down to 6-10 megabyte/s write speed, whereas 3.0 seem to 
> give me 100+ megabyte/s with the exact same workload, I've seen up to 150 
> megabyte/s writes at good times. This is on a box with AES-NI, so the 
> crypto is not the limiting factor.

That is an amazing improvement.  I wish I know what caused it I really have
no idea.  You have quite a deep stack there and the change could be anywhere.

Still, it is good to hear such positive reports - thanks!

NeilBrown


> 
> I have from time to time sent out an email regarding my page allocation 
> failures, but never really got any takers on trying to fault find it, my 
> tickets with ubuntu also never got any real attention. I haven't really 
> pushed it super hard with 3.0, but I've thrown loads at it that would make 
> 2.6.38 lock up.
> 
> Just wanted to send in this success report that this finally seem to have 
> seen some really nice improvements!
> 

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