Re: poor nfs performance & hangs with latest kernels

[Rich <rich@hq.vsaa.lv>]

Neil Brown wrote:
> On Monday February 19, rich@hq.vsaa.lv wrote:
...
>> when there is some intensive nfs activity (write), all other nfs 
>> operations slow down to crawl or even stop at all during that time.
>>
>> i have been able to reproduce the problem with kernel versions 
>> 2.6.16.40, 2.6.19.2 and 2.6.20 (on  slackware-11.0).
>> another person reproduced the hang with 2.6.19-1.2911.fc6 (fedora core 6).
> 
> Are there any kernels where you cannot reproduce the problem?

well, now that my localhost tests are invalidated, i will have to do 
additional testing :)

...
>> export a local directory. i'm using 
>> localhost(rw,no_root_squash,sync,no_subtree_check).
>> mount it locally and try to perform a write operation :
>> dd if=/dev/zero of=/mounted_nfs/testfile bs=512k count=2048
> 
> This scenario is known to cause problems, is very hard to fix, and is
> a case of "well don't do that then".  The problems here are probably
> unrelated to the problems you are having between separate machines.

there i was, hoping to have found a reliable method to reproduce the 
problem...
btw, what's the main cause for this problem ? could it also be observed 
on fast networks or is it limited to cases when server & client are on 
the same machine ?

>> using 2.6.16.21, i was unable to hang my workstation, but server, even 
>> though it survived the test, is still having excessive load (~ 4). top 
>> lists as most resource hungry processes nfsd, kjournald and
>> kblockd.
> 
> So 2.6.16.21 survives but 2.6.16.40 doesn't?  Is that a reliable
> result?  Is that with separate server and client, or server and client
> on the same machine?

most tests were done on a single machine (3 different ones, though), 
after i observed initial problems between several clients and single 
server. so now i will have to redo all the tests with separate client & 
server machines :)

> NeilBrown
-- 
  Rich

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