Re: BUG: Slowdown on 3000 socket-machines tracked down

From: Christian Schmid
Date: Thu Mar 10 2005 - 14:34:31 EST

Attached an image here so you can see whats happening. One pixel are 2 seconds. You can see a small speed-up before the slow-down. This is where I changed lower_zone_protection from 1024 to 0. So it seems its speeding up until the memory is full. Then it drastically slows-down until I set it to 1024 again. then it goes up slowly but not linear (interesting smoothly) until it peaks again at 82 MB/Sec.

PS: 82 MB/sec is not our bandwidth-limit. It still peaks there. Dont know why. Certainly not the drives. They work up to 200 MB/Sec (10 drives there).


Andrew Morton wrote:
Christian Schmid <webmaster@xxxxxxxxxxxxxx> wrote:

> So, maybe a VM problem? That would be a good place to focus since
> I think we can be fairly certain it isn't a problem in just the
> networking code. Otherwise, my tests would show lower bandwidth.

Thanks to your tests I am really sure that its no network-code problem anymore. But what I THINK it is: The network is allocating buffers dynamically and if the vm doesnt provide that buffers fast enough, it locks as well.

Did anyone have a 100-liner which demonstrates this problem?

The output of `vmstat 1' when the thing starts happening would be interesting.

PNG image