Re: [patch] SMP alternatives

[Daniel Jacobowitz <dan@debian.org>]

On Wed, Nov 23, 2005 at 02:19:08PM -0800, Linus Torvalds wrote:
> 
> 
> On Wed, 23 Nov 2005, Daniel Jacobowitz wrote:
> > 
> > I don't think I see the point.  This would let you optimize for the
> > "multi-threaded, but hasn't created any threads yet" or even
> > "multi-threaded, but not right now" cases.  But those really aren't the
> > interesting case to optimize for - that's the equivalent of supporting
> > CPU hotplug.
> 
> NO.
> 
> There is not a _single_ compiler that is multi-threaded, and I'd argue 
> that there probably never will be. It's pointless.
> 
> There's a _lot_ of really performance-sensitive stuff that will NEVER EVER 
> be threaded. You may run a hundred copies of them at the same time, but 
> every single copy will be single-threaded.
> 
> And this will optimize that case in a BIG way.
> 
> This is _not_ about "CPU hotplug". This is _not_ about "threaded apps 
> before they are threaded". This is all about the fact that serious 
> computation is done single-threaded, and anybody who thinks that 
> single-threading is going away is so totally out to lunch that it's not 
> even fun.

I get the feeling you didn't read my message at all.  Let me try it
again.

Why should we use a silicon based solution for this, when I posit that
there are simpler and equally effective userspace solutions?

-- 
Daniel Jacobowitz
CodeSourcery, LLC