Re: [rfc][patch] queued spinlocks (i386)

[Nikita Danilov]

Nick Piggin writes:
 > On Fri, Mar 23, 2007 at 11:04:18AM +0100, Ingo Molnar wrote:
 > > 
 > > * Nick Piggin <npiggin@xxxxxxx> wrote:
 > > 
 > > > Implement queued spinlocks for i386. [...]
 > > 
 > > isnt this patented by MS? (which might not worry you SuSE/Novell guys, 
 > > but it might be a worry for the rest of the world ;-)
 > 
 > Hmm, it looks like they have implemented a system where the spinning
 > cpu sleeps on a per-CPU variable rather than the lock itself, and
 > the releasing cpu writes to that variable to wake it.  They do this
 > so that spinners don't continually perform exclusive->shared
 > transitions on the lock cacheline. They call these things queued
 > spinlocks.  They don't seem to be very patent worthy either, but

Indeed, this technique is very well known. E.g.,
http://citeseer.ist.psu.edu/anderson01sharedmemory.html has a whole
section (3. Local-spin Algorithms) on them, citing papers from the 1990
onward.

Nikita.

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