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Re: fork performance

On 23/10/2012, at 10:26 AM, David Laight <> wrote:

> On Tue, Oct 23, 2012 at 07:41:51AM +1300, Lloyd Parkes wrote:
>> I have taken 30 second ktrace from cvs 1.12.13 that shows fork
>> taking a quarter of a second every time.
> Was that before it returned in the parent, or in the child?

This is in the parent.

> I've seen issues in the past (wasn't actually NetBSD) where the child
> was scheduled before the parent (dunno which NetBSD schedules first)
> and if the child didn't block the parent's priority slowly got lower
> and lower (if the system was busy).

My test system is a VirtualBox guest with two CPUs so scheduling shouldn't get 
this pathological. The VirtualBox host has hyperthreading, so I can't guarantee 
two real CPUs though.

>> This was after cvs had been running for about 12 hours on this task and it
>> didn't occur to me to get a copy of its memory map before I killed it.
> Did you even look at the size?
> Might have been growing a lot.

I checked swap and it wasn't being used. The system had enough RAM for the task 
at hand and not much more. In fact I had to tune the vm sysctl stuff to avoid 
swapping. The system now tries to keep much more anonymous memory in RAM and I 
also reduced the target inactive percentage to 10% for no good reason just 
before the horrendous CVS 1.12.13 test run.

Since this is VirtualBox guess, I can just fire it up again if anyone wants 
more information.


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