Re: elevator=as, or actually gpm doesn't get time from scheduler???

From: Helge Hafting
Date: Mon Apr 19 2004 - 08:47:01 EST

Antti Lankila wrote:
In response to Nick Piggin's:

The only other problems I can think of that you might be
having are chipset problems, or CPU scheduler problems.
Which reminds me, do you have your X server at nice 0?

X has been reniced to zero. But hey! I was doing "cat /dev/psaux" when mouse
stopped moving in X, and I _did_ see data coming from /dev/psaux! So this is
a major update to my understanding of the problem.

But make no mistake, I have been doing this cat /dev/psaux test earlier and
at that time I did _not_ see chars coming out of psaux when the mouse
stopped. That is why I thought I had established that the problem is in the
kernel. I must retest this on the other machines involved when I get to
their consoles next week. I can not explain why this time psaux appears to
work regardless of the userland mouse stall, so for now I must assume some
other factor confused the cat /dev/psaux test at that time.

My X reads gpmdata, so perhaps that's the problem? I now undercut gpm in
order to examine the situation, and my system behaves _perfectly_ as far as
I can see. The mouse issues are all gone. (gpm is still running in the
background, X just reads psaux directly. As I have understood, this is
possible in 2.6 while in 2.4 it caused a problem for multiple readers.)

Gpm might be a problem in high-load situations, for two reasons:

1. gpm is another process. The mouse moves, it takes some time before gpm
gets to read it because the cpu is busy. Then it pass stuff onto the
fifo that X reads from, but now X waits for a while because so much is going on.
2. You may play with the priority of x in order to get better response, but
this does not affect the priority of gpm.

With X reading psaux directly, you avoid some waiting. And X may get a priority
boost for waiting for the mouse to move. With gpm this bonus goes to gpm which
may have a lot less to do with it.

Helge Hafting

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