Re: [PATCH] Performance regression in 2.6.7-rc3

[Linus Torvalds <torvalds@osdl.org>]

On Wed, 16 Jun 2004, Herbert Xu wrote:
>
> Martin J. Bligh <mbligh@aracnet.com> wrote:
> > 
> > How the hell can that have any effect on non-threaded workloads? Perhaps
> > some part of kernel compile *is* multi-threaded. It does seem to get 
> 
> make(1) with vfork(2) perhaps?

Very likely. And in the vfork() case it is definitely WRONG to try to
reschedule (either threads _or_ processes), since the parent is going to
go to sleep real soon now.

I think this code:

                        if (clone_flags & CLONE_VM)
                                wake_up_forked_thread(p);
                        else
                                wake_up_forked_process(p);

is just wrong, and it should be replaced with

			wake_up_new_process(p, clone_flags);

and then "wake_up_new_process()" can do the right thing, which is 
basically:

	if (clone_flags & CLONE_VFORK)
		synchronous wakeup, same as pipe-will-block case
	else if (clone_flags & CLONE_VM)
		thread-wakeup-case
	else
		process-wakeup-case

No?

		Linus