linux-kernel - Re: [patch] CFS scheduler, -v19

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Date:	Tue, 17 Jul 2007 13:37:16 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Markus <lists4me@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [patch] CFS scheduler, -v19



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
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