On Tuesday 23 August 2005 14:17, linux-os \(Dick Johnson\) wrote:
>
> On Mon, 22 Aug 2005, Robert Hancock wrote:
>
> > linux-os (Dick Johnson) wrote:
> >> I reported thet sched_yield() wasn't working (at least as expected)
> >> back in March of 2004.
> >>
> >> for(;;)
> >> sched_yield();
> >>
> >> ... takes 100% CPU time as reported by `top`. It should take
> >> practically 0. Somebody said that this was because `top` was
> >> broken, others said that it was because I didn't know how to
> >> code. Nevertheless, the problem was not fixed, even after
> >> schedular changes were made for the current version.
> >
> > This is what I would expect if run on an otherwise idle machine.
> > sched_yield just puts you at the back of the line for runnable
> > processes, it doesn't magically cause you to go to sleep somehow.
> >
>
> When a kernel build is occurring??? Plus `top` itself.... It damn
> well sleep while giving up the CPU. If it doesn't it's broken.
top doesn't run all the time:
# strace -o top.strace -tt top
14:52:19.407958 write(1, " 758 root 16 0 104 2"..., 79) = 79
14:52:19.408318 write(1, " 759 root 16 0 100 1"..., 79) = 79
14:52:19.408659 write(1, " 760 root 16 0 100 1"..., 79) = 79
14:52:19.409001 write(1, " 761 root 18 0 2604 39"..., 74) = 74
14:52:19.409342 write(1, " 763 daemon 17 0 108 1"..., 78) = 78
14:52:19.409672 write(1, " 773 root 16 0 104 2"..., 79) = 79
14:52:19.410010 write(1, " 774 root 16 0 104 2"..., 79) = 79
14:52:19.410362 write(1, " 775 root 16 0 100 1"..., 79) = 79
14:52:19.410692 write(1, " 776 root 16 0 104 2"..., 79) = 79
14:52:19.411136 write(1, " 777 daemon 17 0 108 1"..., 86) = 86
14:52:19.411505 select(1, [0], NULL, NULL, {5, 0}) = 0 (Timeout)
hrrr..... psssss.......
14:52:24.411744 time([1124797944]) = 1124797944
14:52:24.411883 lseek(4, 0, SEEK_SET) = 0
14:52:24.411957 read(4, "24822.01 18801.28\n", 1023) = 18
14:52:24.412082 access("/var/run/utmpx", F_OK) = -1 ENOENT (No such file or
directory)
14:52:24.412224 open("/var/run/utmp", O_RDWR) = 8
14:52:24.412328 fcntl64(8, F_GETFD) = 0
14:52:24.412399 fcntl64(8, F_SETFD, FD_CLOEXEC) = 0
14:52:24.412467 _llseek(8, 0, [0], SEEK_SET) = 0
14:52:24.412556 alarm(0) = 0
14:52:24.412643 rt_sigaction(SIGALRM, {0x4015a57c, [], SA_RESTORER,
0x40094ae8}, {SIG_DFL}, 8) = 0
14:52:24.412747 alarm(1) = 0
However, kernel compile shouldn't.
I suggest stracing with -tt "for(;;) yield();" test proggy with and without
kernel compile in parallel, and comparing the output...
Hmm... actually, knowing that you will argue to death instead...
# cat t.c
#include <sched.h>
int main() {
for(;;) sched_yield();
return 0;
}
# gcc t.c
# strace -tt ./a.out
...
15:03:41.211324 sched_yield() = 0
15:03:41.211673 sched_yield() = 0
15:03:41.212034 sched_yield() = 0
15:03:41.212400 sched_yield() = 0
15:03:41.212749 sched_yield() = 0
15:03:41.213126 sched_yield() = 0
15:03:41.213486 sched_yield() = 0
15:03:41.213835 sched_yield() = 0
15:03:41.214220 sched_yield() = 0
15:03:41.214577 sched_yield() = 0
15:03:41.214939 sched_yield() = 0
I start "while true; do true; done" on another console...
15:03:43.314645 sched_yield() = 0
15:03:43.847644 sched_yield() = 0
15:03:43.954635 sched_yield() = 0
15:03:44.063798 sched_yield() = 0
15:03:44.171596 sched_yield() = 0
15:03:44.282624 sched_yield() = 0
15:03:44.391632 sched_yield() = 0
15:03:44.498609 sched_yield() = 0
15:03:44.605584 sched_yield() = 0
15:03:44.712538 sched_yield() = 0
15:03:44.819557 sched_yield() = 0
15:03:44.928594 sched_yield() = 0
15:03:45.040603 sched_yield() = 0
15:03:45.148545 sched_yield() = 0
15:03:45.259311 sched_yield() = 0
15:03:45.368563 sched_yield() = 0
15:03:45.476482 sched_yield() = 0
15:03:45.583568 sched_yield() = 0
15:03:45.690491 sched_yield() = 0
15:03:45.797512 sched_yield() = 0
15:03:45.906534 sched_yield() = 0
15:03:46.013545 sched_yield() = 0
15:03:46.120505 sched_yield() = 0
Ctrl-C
# uname -a
Linux firebird 2.6.12-r4 #1 SMP Sun Jul 17 13:51:47 EEST 2005 i686 unknown
unknown GNU/Linux
--
vda
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