> On Feb 5, 2015, at 1:13 PM, Adrian Chadd <adr...@freebsd.org> wrote: > > On 5 February 2015 at 11:03, Sean Bruno <sbr...@ignoranthack.me > <mailto:sbr...@ignoranthack.me>> wrote: >> >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA512 >> >> 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". >> >> PMC: [FR_RETIRED_X86_INSTRUCTIONS] Samples: 267614 (100.0%) , 12350 >> unresolved > > UHm, on a recent intel, use CPU_CLK_UNHALTED instead, so you get an > idea of which instructions are spending the most time doing "stuff". > Some instructions are costlier than others (eg things that cause > memory bus stalls.) > >> %SAMP IMAGE FUNCTION CALLERS >> 5.5 kernel in_cksumdata in_cksum_skip > > .. we're checksumming localhost tcp? :)
Of course we are. The more damning part is the 7.0% of samples that pf consumes. Jim > > -adrian > >> 5.0 kernel tcp_output tcp_do_segment:4.2 tcp_usr_rcvd:0.5 >> 4.6 kernel __rw_wlock_hard tcp_usr_send:3.7 tcp_usr_rcvd:0.8 >> 3.8 pf.ko pf_test pf_check_in:2.0 pf_check_out:1.8 >> 3.6 kernel sched_idletd fork_exit >> 3.2 pf.ko pf_test_state_tcp pf_test >> 3.1 kernel bzero pf_test:0.8 pf_test_state_tcp:0.7 >> 3.1 kernel bcopy m_copydata:1.3 tcp_addoptions:0.7 >> tcp_dooptions:0.5 >> 2.7 kernel tcp_do_segment tcp_input >> >> >> sean >> -----BEGIN PGP SIGNATURE----- >> Version: GnuPG v2 >> >> iQF8BAEBCgBmBQJU075kXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9w >> ZW5wZ3AuZmlmdGhob3JzZW1hbi5uZXRCQUFENDYzMkU3MTIxREU4RDIwOTk3REQx >> MjAxRUZDQTFFNzI3RTY0AAoJEBIB78oecn5kc4kH/02ttXzvapAG2PSML9Ml0Kwf >> XblpOHnrhUU8jsTauGhh8q4C94rb9hFDCzL4cEAI87QMXoBQHi9CWE0v/XdeR+8M >> ajpHlNyd78XbmIKOVksesYWzLbVFjC0A3emnkH4dUX1XD6tJoihVaUQVcrAbNm+I >> p6Z4yXrOXUP9UxBgkCSe5m3Y/K3vcmIPvFSnO/nN/2tckEh6+uuj1n3QyFXkUJJg >> 9erFanvDXr3nOyR6IWXIKxuy1yta32SpOPxywIl81qSBh1n/IOor41WqpzOnlNdM >> d0np+ZD/d+Z9OQJZnuJunCrV6Cv2EFKJe5qBzCdOjLj0KvpNDnFXyndWpeXyvgI= >> =+FSJ >> -----END PGP SIGNATURE----- >> >> >> _______________________________________________ >> freebsd-net@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-net >> To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" > _______________________________________________ > freebsd-net@freebsd.org <mailto:freebsd-net@freebsd.org> mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > <http://lists.freebsd.org/mailman/listinfo/freebsd-net> > To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org > <mailto:freebsd-net-unsubscr...@freebsd.org>" _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
