Monday, September 20, 2010

Proccess Kernel States (wchan in ps)

FreeBSD has a nice feature that will signal a process with SIG-INFO when you press Ctrl-T and will tell you some other interesting data about the process such as the load of the CPU, current command that is being run, and the kernel state the process is in (the wchan keyword in ps(1)).
This state is set by the msleep function and is a syscall or lock that the proccess is waiting on

I know of no other list explaining each of these states so here it goes:

biord: block on io read.
futex: [Linux emulation] process is waiting until a futex is released (see fast userspace mutex)
getblk: get block (seems to be generated often by tar)
nanoslp: process is sleeping for some number of nanoseconds (see nanosleep(2))
pause: process is waiting for a signal (see pause(3))
pcmwrv: waiting for audio samples to be played
piperd: read(2) from a pipe
pipewr: write(2) to a pipe
physrd: reading from a HDD
runnable: process is ready to run on the CPU
running: currently on CPU
sbwait: wait for socket to return data (see uipc_sockbuf.c) 
swread: read in from swap
stopev: process is stopped because of a debugging event (see sys_process.c; relates to ptrace(2))
tttout: write(2) to a tty
ttyin: read(2) from a tty
ucond: a proccess is blocked until a pthreads mutex is released
vnread: part of the pager (see vnode_pager.c)
wait: wait(2) for a child process
wdrain: write drain. On a device mounted with the async option (or soft-updates) wait until all the previous writes have been completed. (see vfs_bio.c)
zombie: a process died but its parent did not wait(2) for it.

There are other syscalls that are similar to the ones mentioned above (such as readv(2) instead of read(2), and waitpid(2) instead of wait(2)) which will end up with the same wchans.

Thank you irc:// for helping me figure out what all of these mean.

I will try to keep this list up-to-date as I find out about more of them.

Update 9/21/10: removed "CPU0" state - it doesn't show up in the siginfo output - only in the top output.
Update 9/22/10: added getblk entry without link to syscall
Update 10/7/10: added wdrain, swread - I have a /lot/ more to add. 
I need to add all the following - and more: sfbufa, umtxqb, psleep, qsleep, bo_wwait, bwunpin, sigwait, pause, suspkp suspkp ktsusp  mntref, "mount drain", roothold, rootwait, failpt, exithold, exit1, ritwait , kqflxwt, kqclose, kqclo1, kqclo2, kqkclr, kqflxwt, ithread, iev_rmh , purgelocks, conifhk, aioprn, aiordy, aiospn, aiowc vlruwt vlruwk targrd tgabrt cgticb cgticb  sgread simfree ccb_scanq crydev  crypto_destroy crypto_destroy crypto_ret_wait