On Fri, Aug 03, 2007 at 02:20:10AM +0200, Nick Piggin wrote:

On Thu, Aug 02, 2007 at 11:33:39AM -0700, Martin Bligh wrote:

quoted

Nick Piggin wrote:

quoted

On Wed, Aug 01, 2007 at 03:52:11PM -0700, Martin Bligh wrote:

quoted

quoted

And so forth.  Initial forks will balance.  If the children refuse to
die, forks will continue to balance.  If the parent starts seeing short
lived children, fork()s will eventually start to stay local.  

Fork without exec is much more rare than without. Optimising for
the uncommon case is the Wrong Thing to Do (tm). What we decided

It's only the wrong thing to do if it hurts the common case too
much. Considering we _already_ balance on exec, then adding another
balance on fork is not going to introduce some order of magnitude
problem -- at worst it would be 2x but it really isn't too slow
anyway (at least nobody complained when we added it).

One place where we found it helps is clone for threads.

If we didn't do such a bad job at keeping tasks together with their
local memory, then we might indeed reduce some of the balance-on-crap
and increase the aggressiveness of periodic balancing.

Considering we _already_ balance on fork/clone, I don't know what
your argument is against this patch is? Doing the balance earlier
and allocating more stuff on the local node is surely not a bad
idea.

I don't know who turned that on ;-( I suspect nobody bothered
actually measuring it at the time though, or used some crap
benchmark like stream to do so. It should get reverted.

So you have numbers to show it hurts? I tested some things where it
is not supposed to help, and it didn't make any difference. Nobody
else noticed either.

If the cost of doing the double balance is _really_ that painful,
then we ccould skip balance-on-exec for domains with balance-on-fork
set.

Nick, Even if it is not painful, can we skip balance-on-exec if
balance-on-fork is set. There is no need for double balance, right?

Especially with the optimization you are trying to do with this patch,
balance-on-exec may lead to wrong decision making this optimization
not work as expected.

or perhaps do balance-on-fork based on clone_flags..

thanks,
suresh

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