Re: [PATCH 4/4] nohz: Set isolcpus when nohz_full is set

Afzal Mohammed
2015-05-20T20:38:20Z

Hi,

On Sun, May 17, 2015 at 07:30:50AM +0200, Mike Galbraith wrote:

> Yeah, tying nohz_full set to isolcpus set up an initial condition that
> you have to tear down with cpusets if you want those cpus returned to
> the general purpose pool. I had considered the kernel setting initial
> state to be an optimization, but have reconsidered.

> Given that kernel initiated association to isolcpus, a user turning
> NO_HZ_FULL_ALL on had better not have much generic load to manage. If

On a quad-core desktop system with NO_HZ_FULL_ALL, hackbench took 3x
time as compared to w/o this patch, except boot cpu every one else
jobless. Though NO_HZ_FULL_ALL (afaik) is not meant for generic load,
it was working fine, but not after this - it is now like a single core
system.

Regards
Afzal

> he/she does not have CPUSETS enabled, or should Rik's patch rendering
> isolcpus immutable be merged, he/she would quickly discover that the
> generic box has been transformed into an utterly inflexible specialist
> incapable of performing mundane tasks ever again.