Date: Thu, 5 Feb 2015 12:23:14 -0800 From: hiren panchasara <hiren@strugglingcoder.info> To: Scott Long <scott4long@yahoo.com> Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Silly experiments with netisr Message-ID: <20150205202314.GD69733@strugglingcoder.info> In-Reply-To: <752D84FB-0B65-47CF-973A-91C3697A28DC@yahoo.com> References: <54D3BE67.8060502@ignoranthack.me> <752D84FB-0B65-47CF-973A-91C3697A28DC@yahoo.com>
next in thread | previous in thread | raw e-mail | index | archive | help
[-- Attachment #1 --] On 02/05/15 at 12:31P, Scott Long via freebsd-net wrote: > > > On Feb 5, 2015, at 12:03 PM, Sean Bruno <sbruno@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 [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (FreeBSD) iQF8BAEBCgBmBQJU09ExXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9w ZW5wZ3AuZmlmdGhob3JzZW1hbi5uZXRBNEUyMEZBMUQ4Nzg4RjNGMTdFNjZGMDI4 QjkyNTBFMTU2M0VERkU1AAoJEIuSUOFWPt/lOMcH/A7LKBCskK8AWfqWDcu6ULGp +8rRSwc0gmE0UlZ8yN+QTwACXMf41Lw8p1KydOBIuyK5HelkumqBiank9Xwecyim AGpNiynsqFmbXQ8NeM6oJuJNbn7JZyVz+bSSKuzSoWT1uJ5I1poXcZDIt3f2E+Si i4FjiTshlec4AqMIC1w4WcbJ73H+AuMVQQEnPEXGWYRTlFEfALLSOBtiLQqOaXqc aFBgv6qtZa4AS5t7Wyf6QxfwcV8wtNfK0HHRxpNyzvQioj0Lgy+tb2SybDL97bWB SRkh9VgU+ymbbJfid6nBZaS6m7dILV4l8e0V4/0L8KvnWyUeWFUmFRsGwcDgw9g= =Nymf -----END PGP SIGNATURE-----
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20150205202314.GD69733>