On 02/05/15 at 12:31P, Scott Long via freebsd-net wrote: > > > On Feb 5, 2015, at 12:03 PM, Sean Bruno <sbr...@ignoranthack.me> wrote: > > > > > > Signed PGP part > > Some questions came up around the office and we ended up doing some > > quite silly things with lo0 and netcat. > > > > If one runs a continuous netcat on localhost to another netcat listener > > on localhost that writes the output to /dev/null, netisr gets super busy > > doing stuff/things. > > > > E.g. > > -- listener running "nc -k -l 10000 > /dev/null" > > - sender running in a while loop "nc -N localhost 10000 < > > /var/tmp/testfile" > > > > Interesting things start happening on the machine. top -SH shows netisr > > eating up about 1/2 of a cpu core. If you drop the MTU on lo0 to 1500 > > (so that it looks like something in the real world), netisr will peg out > > a cpu core. This seems logical, in that smaller MTU means busier > > netisr. Its interesting though. > > > > Looking at some pmcstat things, shows that the system is busilly > > chugging along in tcp_do_segment(). I wonder if this is meaningful in > > anyway or just "interesting". > > > Welcome to our workload. Granted, we don?t involve pf, but the majority of > our CPU processing right now is spent in TCP (with the rest being spent in > the VM, but that?s a different matter). > > FWIW, Randall has some optimizations in this area of the stack. They aren?t > huge, IIRC they?re only a few percent, but worth looking at. Scott,
It'd be great if you guys can share it. And yes, any small persentage would help :-) cheers, Hiren
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