Re: Increased Latencies when upgrading kernel version
From: Eric Dumazet
Date: Thu Apr 01 2010 - 17:19:20 EST
Le jeudi 01 avril 2010 Ã 14:12 -0500, Taylor Lewick a Ãcrit :
> For some time now we've been running an older kernel, 188.8.131.52. When
> we tried to upgrade, first going to 184.108.40.206 and then to 220.127.116.11 and
> 18.104.22.168 we noticed that latencies increased. At first we noticed it
> by doing network tests via udpping, netperf, etc. We made some
> tweaks, and were able to get network latency to within 1 to 2
> microseconds of where we were previously on 22.214.171.124. Then we did
> some more testing, and noticed that system latency also seems higher.
> We've done our tests on identical hardware servers, same NICs,
> connected through same network gear. Basically, we've tried to keep
> everything identical except the kernel versions, and we are unable to
> achieve the same performance for system latency on the newer kernels,
> despite adjusting various kernel settings and recompiling.
> The latency differences are about 15 microseconds per transaction.
> At this point, I don't know what else to try. I haven't played around
> with the /proc/sys/kernel/sched_* paramaters under the newer kernels
> yet. Have tried changing pre-emption modes with little effect, in
> fact, voluntary preemption seems to be peforming the best for us.
> At this time the realtime patch isn't really an option for us to
> consider, at least not yet.
> Any suggestions? Is this a known issue when upgrading to more recent
> kernel versions?
Well, this is bit difficult to generically answer to your generic
question. 15 us more latency per transaction seems pretty bad.
Some inputs would be nice, describing your workload and
ethtool -S eth0
ethtool -c eth0
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/