Date: Thu, 5 Feb 2015 12:31:57 -0700 From: Scott Long <scott4long@yahoo.com> To: sbruno@freebsd.org Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Silly experiments with netisr Message-ID: <752D84FB-0B65-47CF-973A-91C3697A28DC@yahoo.com> In-Reply-To: <54D3BE67.8060502@ignoranthack.me> References: <54D3BE67.8060502@ignoranthack.me>
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--Apple-Mail=_0FF2A146-5C2F-4C87-AC39-B784AF05DE53 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Feb 5, 2015, at 12:03 PM, Sean Bruno <sbruno@ignoranthack.me> = wrote: >=20 >=20 > Signed PGP part > Some questions came up around the office and we ended up doing some > quite silly things with lo0 and netcat. >=20 > 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. >=20 > E.g. > -- listener running "nc -k -l 10000 > /dev/null" > - sender running in a while loop "nc -N localhost 10000 < > /var/tmp/testfile" >=20 > 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. >=20 > 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=E2=80=99t 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=E2=80=99s a different matter). FWIW, Randall has some optimizations in this area of the stack. They = aren=E2=80=99t huge, IIRC they=E2=80=99re only a few percent, but worth = looking at. Scott --Apple-Mail=_0FF2A146-5C2F-4C87-AC39-B784AF05DE53 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQEcBAEBCgAGBQJU08UtAAoJEIxiMIkw8yo426gH/3DciyuCw+07veEWVKeLdZQq X+8qWGAYtVF6ghx4s0YBpHfR1f4xMT/9YFwounm84otn2xLPPSyrLAH258v/gYtb ZJ7Welj7Z+GJOoUJaRbGGvCFIwWd+dwEKb8FcqDyy0yvGI1W8XoLph9w0Y8hIx9o CCvV2Pv4KF/Ftr584gOZtiRtzsw00BsJ0Q/Q+aOBe4sK7M0eE25rpzvAlG82VP2x fQ+iFa4s6B1ckJ+Wo3ArsLIzh2UprFOIxB+ewlinXLWuMVHQ79wm5fXBiPEfQLq/ OUCCdqcmtytUM+XcogGTwGK2ld4sPYDxi9Jp98DnPYcbtKDHsX80mrW/nY6Vt2o= =cVSX -----END PGP SIGNATURE----- --Apple-Mail=_0FF2A146-5C2F-4C87-AC39-B784AF05DE53--
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