Messages in this thread | | | Subject | Re: [PATCH 0/4] Page based O_DIRECT v2 | From | "Alan D. Brunelle" <> | Date | Wed, 19 Aug 2009 15:05:42 -0400 |
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Hi Jens -
I'm not using loop, but it appears that there may be a regression in regular asynchronous direct I/O sequential write performance when these patches are applied. Using my "small" machine (16-way x86_64, 256GB, two dual-port 4GB FC HBAs connected through switches to 4 HP MSA1000s - one MSA per port), I'm seeing a small but noticeable drop in performance for sequential writes on the order of 2 to 6%. Random asynchronous direct I/O and sequential reads appear to unaffected.
http://free.linux.hp.com/~adb/2009-08-19/nc.png
has a set of graphs showing the data obtained when utilizing LUNs exported by the MSAs (increasing the number of MSAs being used along the X-axis). The critical sequential write graph has numbers like (numbers expressed in GB/second):
Kernel 1MSA 2MSAs 3MSAs 4MSAs ------------------------ ----- ----- ----- ----- 2.6.31-rc6 : 0.17 0.33 0.50 0.65 2.6.31-rc6 + loop-direct: 0.15 0.31 0.46 0.61
Using all 4 devices we're seeing a drop of slightly over 6%.
I also typically do runs utilizing just the caches on the MSAs (getting rid of physical disk interactions (seeks &c).). Even here we see a small drop off in sequential write performance (on the order of about 2.5% when using all 4 MSAs)- but noticeable gains for both random reads and (especially) random writes. That graph can be seen at:
http://free.linux.hp.com/~adb/2009-08-19/ca.png
BTW: The grace/xmgrace files that generated these can be found at -
http://free.linux.hp.com/~adb/2009-08-19/nc.agr http://free.linux.hp.com/~adb/2009-08-19/ca.agr
- as the specifics can be seen better whilst running xmgrace on those files.
The 2.6.31-rc6 kernel was built using your block git trees master branch, and the other one has your loop-direct branch at:
commit 806dec7809e1b383a3a1fc328b9d3dae1f633663 Author: Jens Axboe <jens.axboe@oracle.com> Date: Tue Aug 18 10:01:34 2009 +0200
At the same time I'm doing this, I'm doing some other testing on my large machine - but the test program has hung (using the loop-direct branch kernel). I'm tracking that down...
Alan D. Brunelle Hewlett-Packard
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