Re: High CPU usage / load average after upgrading to Ubuntu 12.04

On 20/02/13 06:51, Josh Berkus wrote:
> On 02/18/2013 08:28 PM, Mark Kirkwood wrote:
>> Might be worth looking at your vm.dirty_ratio, vm.dirty_background_ratio
>> and friends settings. We managed to choke up a system with 16x SSD by
>> leaving them at their defaults...
> Yeah? Any settings you'd recommend specifically? What did you use on
> the SSD system?
>

We set:

vm.dirty_background_ratio = 0
vm.dirty_background_bytes = 1073741824
vm.dirty_ratio = 0
vm.dirty_bytes = 2147483648

i.e 1G for dirty_background and 2G for dirty. We didn't spend much time
afterwards fiddling with the size much. I'm guessing the we could have
made it bigger - however the SSD were happier to be constantly writing a
few G than being handed (say) 50G of buffers to write at once . The
system has 512G of ram and 32 cores (no hyperthreading).

regards

Mark