Subject: Re: [RFC] [PATCH] allow low HZ values?

From: Andi Kleen <[email-masked]>
Date: Tue, 12 Oct 2010 16:31:20 +0200

Thomas Gleixner <[email-masked]> writes:

> On Mon, 11 Oct 2010, Tim Pepper wrote:
>
>> I'm not necessarily wanting to open up the age old question of "what is
>> a good HZ", but we were doing some testing on timer tick overheads for
>> HPC applications and this came up...
>
> Yeah. This comes always up when the timer tick overhead on HPC is
> tested. And this patch is again the fundamentally wrong answer.

That's a unfair description of the proposal.

> We have told HPC folks for years that we need a kind of "NOHZ" mode
> for HPC where we can transparently switch off the tick when only one
> user space bound thread is active and switch back to normal once this
> thing terminates or goes into the kernel via a syscall. Sigh, nothing
> happened ever except for repeating the same crap patches over and
> over.

Jan Blunck posted a patch for this exactly few months ago.
Unfortunately it didn't get the accounting right, but other than
that it seemed like a reasonable starting point.

-Andi
-- 
[email-masked] -- Speaking for myself only.