[OpenIndiana-discuss] Are there any known problems with OI and jumbo frames MTU 9000

[Jim Klimov]

On 2013-01-14 12:41, Flo wrote:
> My question:
> Do I get a performance gain with a MTU size of 9000 and are there known
> issues with OpenIndiana, link-aggregation and a MTU size of 9000?


Likely yes, there should be a gain - although some experts on the list
have recently stated, that with modern hardware the difference should
be negligible. In the past it could have been greater due to slower
NIC processors, I suppose.

 From my experience with Jumbo on e1000 interfaces, there are flags
you should set in the driver config file (and reapply after each OS
upgrade which overwrites this file):

# diff /kernel/drv/e1000g.conf-orig /kernel/drv/e1000g.conf-jumbo
52c52,53
< MaxFrameSize=0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0;
---
 > #MaxFrameSize=0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0;
 > MaxFrameSize=3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3;


Or to test without LSO (dunno why we have this, maybe hunted for bugs?)

# diff /kernel/drv/e1000g.conf-orig /kernel/drv/e1000g.conf-jumbo-noLSO
52c52,53
< MaxFrameSize=0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0;
---
 > #MaxFrameSize=0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0;
 > MaxFrameSize=3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3;
84a86,88
 >
 >       #Disable LSO in e1000g.conf by adding one line:
 > lso_enable = 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0;


On my OI boxes I see that the default flag value is still zero...


After you set these flags to 3 and reboot, you can use the increased
frame sizes in "ifconfig ... mtu" clauses.

Also take care to verify that all the NICs and switches and OSes on
each side do indeed support your chosen frame size (i.e. 9000 bytes),
because there were many different maximum "increased frame sizes"
supported over time. By using no more than the lowest common size
supported by all your gear, you'd avoid packet fragmentation and/or
errors and benefit from Jumbo.

Good luck,
//Jim