Robert Watson wrote:
On Thu, 15 Oct 2009, rihad wrote:
meaning that USABLE_TX_BD is expected to be smaller than MAX_TX_BD.
What if MAX_TX_BD is itself way smaller than 1024, which I'll
eventually set ifq_drv_maxlen to? Can a driver guru please comment on
this? In a few days I'm going to try it anyway, and if the system
locks up I'll just revert back to the original code, and order a darn
expensive Intel 10 Gige card, but it won't hurt to ask beforehand.
Depending on your tolerance for experimentalism, it might be useful to
use DTrace to confirm our interpretation of events. The way I'd do this
is to add an instrumentation point (using SDT) to the points where the
statistics of interest are getting bumped, and then profile using DTrace
for a bit with the following script:
the:event:name:here
{
@data[stack()] = count();
}
Let it run for 30-60 seconds, and you should get back a report on the
frequency of each possible code path to generate the statistic. We
believe that the drops are a result of bursts of packets from dummynet,
in which case the dominant trace should be to dummynet timers. It would
be interesting to see if that's right.
Thanks, but as I haven't ever played with DTrace before, but for the
sake of FreeBSD and for our own sake, could you or someone else provide
me with a step-by-step tutorial on how to do exactly that? I hear
GENERIC kernel lacks DTrace support, so I must rebuild it with
KDTRACE_HOOKS enabled? Does such support hurt normal performance while
dtrace is not being used? I'm a bit afraid of experimenting on a
production box belonging to a business I do not own.
Meanwhile today I've emailed David Christensen <davi...@broadcom.com>
mentioned in the bce source code, asking him if it's ok to change that
value.
If I get a chance, I'll spend a few minutes today looking at a more
general patch to make it easy to use DTrace with network stack error
points.
Robert
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