On Wed, Jan 16, 2002 at 02:48:25PM -0500, Chris Wright wrote: > i need something that is nearer to 1/1000th of a second resolution. Sounds like you need the POSIX real-time stuff. sigaction, nanosleep, and similar. > however, i am curious: if you have a task that runs for half a jiffy, > then get blocked, does the kernel switch to a new task immediatly, or > does it wait for the jiffy to expire before continuing (wasting half a > jiffy). The Linux kernel can switch to another task when exiting kernel mode and when it blocks in kernel code. This is the HZ (100 per second on x86 by default) interrupt, real-time-clock interrupts, keyboard, mouse, NIC, etc interrupts. This is also blocking while waiting for page faults, reading/writing to disk that isn't in the buffer cache yet, reading from terminals .. all the things that can cause a process to block. :) The vmstat program can give you some details on this.. $ vmstat 1 procs memory swap io system cpu r b w swpd free buff cache si so bi bo in cs us sy id 1 0 0 73268 1408 8352 240944 0 0 9 8 5 10 18 1 25 1 0 0 73268 1404 8352 240944 0 0 0 0 157 698 2 1 97 1 0 0 73268 1408 8352 240944 0 0 0 0 178 771 1 0 99 0 0 0 73268 1404 8352 240944 0 0 0 0 188 823 0 1 99 (I sure hope that didn't wrap...) Note the 'cs' column .. it shows context switches per second, while 'in' shows interrupts per second. Cheers ;) -- People who separate manpages from the programs they document would steal sheep. -- apologies to Goudy
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