Re: xterm scrolling speed - scheduling weirdness in 2.6 ?!

From: Nick Piggin <piggin@cyberone.com.au>
To: Peter Osterlund <petero2@telia.com>
Cc: Con Kolivas <kernel@kolivas.org>,
	Tim Connors <tconnors+linuxkernel1073186591@astro.swin.edu.au>,
	linux-kernel@vger.kernel.org, efault@gmx.de
Subject: Re: xterm scrolling speed - scheduling weirdness in 2.6 ?!
Date: Tue, 06 Jan 2004 17:27:11 +1100	[thread overview]
Message-ID: <3FFA553F.3040202@cyberone.com.au> (raw)
In-Reply-To: <m2ekudq080.fsf@telia.com>

Peter Osterlund wrote:

>Nick Piggin <piggin@cyberone.com.au> writes:
>
>
>>Peter Osterlund wrote:
>>
>>
>>>But the scheduler is also far from fair in this situation. If I run
>>>
>>snip a good analysis...
>>
>>... but fairness is not about a set of numbers the scheduler gives to
>>each process, its about the amount of CPU time processes are given.
>>
>>In this case I don't know if I find it objectionable that X and xterm
>>are considered interactive and perl considered a CPU hog. What is the
>>actual problem?
>>
>
>The problem is that if perl would get only slightly more cpu time, it
>would get ahead of xterm, which would make this test case run
>something like 10 times faster than it currently does. (Because xterm
>switches to jump scrolling when it can't keep up.)
>
>I guess it would be possible to fix this by introducing a
>usleep(10000) at some strategic place in the xterm source code, but I
>still find it strange that two tasks eating 40% cpu time each are
>considered interactive, while a task eating 4% is considered a cpu
>hog, especially since the 4% task never got a chance to prove that it
>didn't want to steal all cpu time. All that was proven was that it
>wanted more than 4% of the cpu.
>
>Also, while my test case runs, other tasks (such as running "ps" from
>a network login) are very slow, at least until the extra load makes
>the scheduler realize that the two tasks eating most of the cpu time
>should not have maximum priority bonus.
>

This is what top looks like with my (now fixed) scheduler
(priorities go from 0 to 59). In theory I guess it looks like what
you want.

  920 root      21 -10 88156  17m  79m S 50.8  7.0  11:08.47 XFree86
16762 npiggin   40   0  4804 2396 4356 R 37.9  0.9   0:07.76 xterm
16784 npiggin   23   0  3128 1212 2664 S  9.3  0.5   0:01.93 perl

xterm is a CPU hog, XFree86 is half and half, perl is at close to highest
priority (which is 20 for a nice 0 process). When using xterm without jump
scrolling, it seems to mess up X's scheduler by flooding it with so many
small requests.