Concluding the SMPng project

Chris H. fbsd at
Mon Jun 12 21:12:40 UTC 2006

Quoting Kris Kennaway <kris at>:

> Several of us have been discussing recently whether it is time to
> bring the SMPng project to a formal conclusion.
> According to the SMPng project webpage,
>  "The end goal of the SMPng Project is to decompose the Giant lock
>  into a number of smaller locks, resulting in reduced contention (and
>  improved SMP performance)."
> Thanks to the hard work of many developers over the past ~6 years, this
> goal is now complete.
> While Giant has not been completely eliminated from the kernel and
> several subsystems are still giant-locked (notably ipv6, tty, and CAM,
> although work is in progress on all of these fronts), kernel profiling
> traces show that for many real-world application loads the Giant lock
> is simply no longer a factor in the performance of the SMP kernel.
> See e.g.
> for one such measurement of the extent of Giant locking in FreeBSD
> 6.x; other real-world application workloads are similar.
> Some of the benefits of formally concluding the SMPng project are:
> * The focus of SMP development work has largely changed from "break up
> Giant everywhere" to "carefully measure the effects of the locking
> decisions that were made, and optimize for greater performance and
> scalability".  This is a major milestone and should be announced to
> the world, perhaps under the banner of a new "FreeBSD Scalability
> Project".
> * For example, a number of us are looking very closely at the nascent
> FreeBSD port to the Sun Ultrasparc T1, which provides 32 virtual CPUs
> (4 threads on 8 CPU cores) on a single chip.  Optimizing for the new
> generation of SMP hardware is going to be a major effort over the
> coming year.

Ahh, so the contributions made by the PIII & PIV CPU's were merely to
obtain access to the Sparc systems, and the PIII & PIV will be relegated
to the ubiquitous I386 scrap heap, as the future and ultimate goal of
FreeBSD is to be Sun Microsystems. Pitty, FreeBSD has always provided
such wide scalability. So easy to implement on so many architectures.
I wish I had known it's agenda years ago. As I would not have spent
so many years and so many dollars building *BSD based infrastructures.
Perhaps I've misunderstood this announcement. But if not;
good riddance.

> * We get to draw a line under the significant architectural changes of
> the past 6 years and move forward.  Throughout the 5.x branch I think
> there was still a lot of developer mentality that it represented a
> work in progress, but I think there's a broad consensus that 6.x is
> the natural conclusion of that process, and we have a new baseline
> upon which to build for the future.
> * There were many people who were unsure whether the goals of the
> SMPng project could be realised or whether the tasks that the FreeBSD
> project set for itself were just too ambitious.  While SMP work
> remains ongoing, I think it's fair to say that the project has
> addressed this criticism admirably, and we should not be shy about
> advertising this achievement.
> Kris

Shameless self-promotion follows...
... or does it?

FreeBSD 5.4-RELEASE-p12 (SMP - 900x2) Tue Mar 7 19:37:23 PST 2006

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