On 5 February 2015 at 11:03, Sean Bruno <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? :) -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 mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
