Re: [PATCH 0/10] bulk cpu removal support

[Ashok Raj <ashok.raj@intel.com>]

On Wed, May 10, 2006 at 11:06:06PM -0700, Andrew Morton wrote:
Hi Andrew,

> Shaohua Li <shaohua.li@intel.com> wrote:
> >
> > CPU hotremove will migrate tasks and redirect interrupts off dead cpu.
> 
> This seems an awful lot of code for something which happens so infrequently.
> 
> How big is the problem you're fixing here, and what are the
> user-observeable effects of these changes?

This is useful when say a NUMA node is being removed. With new multi-core
CPUs comming up, considering a 2 core with HT, we could have up to 4 logical
per socket. On NUMA node with 4 sockets, a node removal will mean we 
do 16 single cpu offlines. Each time the process and interrupts could
end up on a CPU that might be removed just immediatly.

The same is also useful for SMP Suspend/resume cases since the logical offline
is same here as well.

Even thought the code changes seem a lot, most of it is just preparation of
functions ready to accept a cpumask_t instead of a single cpu like earlier.
The reason we split them to smaller chunks so the scope of change is well
understood with each patch.

The major changes are

 - stop machine to run cpu offline functions on each cpu going offline
 - prepare offline functions in offline path to take cpumask_t
 - Some task migrate dead lock removal consideration that we ran into
    during stress test.

I know Shaohua ran tests for more than 20+ hrs with the patch, both on i386 
and x86_64.

once we get some time deltas on a bigger machine it will help a lot. 
Iam also trying to check with some OEM';s who have such large machines for
some data.. keep posted.

ashokr

-- 
Cheers,
Ashok Raj
- Open Source Technology Center