Re: [PATCH] Performance regression in 2.6.7-rc3

Linus Torvalds
2004-06-16T03:12:49Z

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