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

[Christian Schmid]

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).

Chris


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.