TSO help or hindrance ? (was Re: TSO and FreeBSD vs Linux)

[Barney Cordoba]

NFS has been broken since Day 1, so lets not come to conclusions about anything
as it relates to NFS.

BC


________________________________
 From: Mike Tancsa <mike at sentex.net>
To: Rick Macklem <rmacklem at uoguelph.ca> 
Cc: FreeBSD Net <net at freebsd.org>; David Wolfskill <david at catwhisker.org> 
Sent: Wednesday, September 4, 2013 11:26 AM
Subject: TSO help or hindrance ?  (was Re: TSO and FreeBSD vs Linux)
 

On 9/4/2013 8:50 AM, Rick Macklem wrote:
> David Wolfskill wrote:
>>
>>
>> I noticed that when I tried to write files to NFS, I could write
>> small
>> files OK, but larger ones seemed to ... hang.
>> * "ifconfig -v em0" showed flags TSO4 & VLAN_HWTSO turned on.
>> * "sysctl net.inet.tcp.tso" showed "1" -- enabled.
>>
>> As soon as I issued "sudo net.inet.tcp.tso=0" ... the copy worked
>> without
>> a hitch or a whine.  And I was able to copy all 117709618 bytes, not
>> just
>> 2097152 (2^21).
>>
>> Is the above expected?  It came rather as a surprise to me.
>>
> Not surprising to me, I'm afraid. When there are serious NFS problems
> like this, it is often caused by a network fabric issue and broken
> TSO is at the top of the list w.r.t. cause.


I was just experimenting a bit with iSCSI via FreeNAS and was a little
disappointed at the speeds I was getting. So, I tried disabling tso on
both boxes and it did seem to speed things up a bit.  Data and testing
methods attached in a txt file.

I did 3 cases.

Just boot up FreeNAS and the initiator without tweaks.  That had the
worst performance.
disable tso on the nic as well as via sysctl on both boxes. That had the
best performance.
re-enable tso on both boxes. That had better performance than the first
case, but still not as good as totally disabling it.  I am guessing
something is not quite being re-enabled properly ? But its different
than the other two cases ?!?

tgt is FreeNAS-9.1.1-RELEASE-x64 (a752d35) and initiator is r254328 9.2
AMD64

The FreeNAS box has 16G of RAM, so the file is being served out of cache
as gstat shows no activity when sending out the file



    ---Mike


-- 
-------------------
Mike Tancsa, tel +1 519 651 3400
Sentex Communications, mike at sentex.net
Providing Internet services since 1994 www.sentex.net
Cambridge, Ontario Canada  http://www.tancsa.com/

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