>>>>> "Andi" == Andi Kleen <[EMAIL PROTECTED]> writes:
Andi> Andrew Morton <[EMAIL PROTECTED]> writes: >> Why does the kernel need this feature? >> >> Have you any numbers on the overhead? Andi> It does RDTSC and lots of complicated stuff twice for each Andi> system call. On P4 this will be extremly slow (> 1000cycles Andi> combined) It is pretty unlikely that whatever it does justifies Andi> this extreme overhead in a critical fast path. Not really `lots of complicated stuff'. Just swap a timer and set a flag on entry: msp->timers[msp->laststate] += now - msp->lastchange msp->lastchange = now msp->laststate = ONCPU_SYS msp->cflags |= MSA_SYS And swap timers and clear the flag on exit. The flag's needed to force return to ONCPU_SYS rather than ONCPU_USR if the task preempted or interrupted while in a system call. If there's a simpler, cheaper, faster way to track time spent in system calls (as opposed to time spent in interrupt handlers, or on the run queue) thn I'd like to know what it is. And I recognise there're are lots of people who don't want this --- but there are some who do. I've maintained this patch since mid 2003, and have seen a steady trickle of downloads --- one or two a week. -- Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au The technical we do immediately, the political takes *forever* - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/