Re: [patch] CFS scheduler, -v19

Linus Torvalds
2007-07-17T20:38:28Z

On Tue, 17 Jul 2007, Ingo Molnar wrote:
>
> i think the problem starts here:
>
> 11902 1184699865.141939 read(3, "", 32) = 0 <0.000007>

Well, it's preceded by a poll() that says that it has a POLLHUP event, so
that socket would seem to have simply been closed from the other end.
There's also a huge amount of select() calls showing the same thing
(except since it's just the input side, you cannot tell that it's
POLLHUP).

Don't ask me *why*, though. It's preceded by

..
11902 1184699848.615201 read(3, 0x7fffb5b9c8b0, 32) = -1 EAGAIN (Resource temporarily unavailable) <0.000009>
11902 1184699848.615252 poll([{fd=3, events=POLLIN, revents=POLLIN}], 1, -1) = 1 <0.009307>
11902 1184699848.624614 read(3, "\1 \303!\0\0\0\0\4\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0b\340T\0\0\0\0\0", 32) = 32 <0.000011>

.. got data ..

11902 1184699848.624710 ioctl(3, FIONREAD, [0]) = 0 <0.000009>
11902 1184699848.624762 ioctl(3, FIONREAD, [0]) = 0 <0.000048>

.. ok, nothing more..

11902 1184699848.624866 select(10, [3 4 5 7 9], [], [], NULL) = 1 (in [3]) <16.495008>
11902 1184699865.119950 ioctl(3, FIONREAD, [0]) = 0 <0.000006>

16+ seconds pass, now it's marked as readable, but returns zero bytes of
data: the other end closed it.

Tons of unnecessary and stupid sequences of:

11902 1184699865.119988 select(10, [3 4 5 7 9], [], [], NULL) = 1 (in [3]) <0.000007>
11902 1184699865.120031 ioctl(3, FIONREAD, [0]) = 0 <0.000005>
..

and then finally:

...
11902 1184699865.141809 poll([{fd=3, events=POLLIN, revents=POLLIN|POLLHUP}], 1, 0) = 1 <0.000005>
11902 1184699865.141838 ioctl(3, FIONREAD, [0]) = 0 <0.000005>
11902 1184699865.141939 read(3, "", 32) = 0 <0.000007>

ie now konqueror noticed that it was *really* closed, and read the EOF.

But why does that happen? And why would the scheduler have *anything* to
do with this? No idea. Maybe timing. Maybe the time.c changes. Dunno.

Linus