Re: [RFC] New locking primitive for 2.5

[Dave Hansen <haveblue@us.ibm.com>]

Andrew Morton wrote:
> Robert Love wrote:
>>On Thu, 2002-02-07 at 10:38, Martin Wirth wrote:
>>Some of the talk I've heard has been toward an adaptive lock.  These are
>>locks like Solaris's that can spin or sleep, usually depending on the
>>state of the lock's holder.  Another alternative, which I prefer since
>>it is much less overhead, is a lock that spins-then-sleeps
>>unconditionally.
> I dunno.  The spin-a-bit-then-sleep lock has always struck me as
> i_dont_know_what_the_fuck_im_doing_lock().  Martin's approach puts
> the decision in the hands of the programmer, rather than saying
> "Oh gee I goofed" at runtime.

The spin-then-sleep lock could be interesting as a replacement for the 
BKL in places where a semaphore causes performance degredation.  In 
quite a few places where we replaced the BKL with a more finely grained 
semapore (not a spinlock because we needed to sleep during the hold), 
instead of spinning for a bit, it would schedule instead.  This was bad 
:).  Spin-then-sleep would be great behaviour in this situation.

-- 
Dave Hansen
haveblue@us.ibm.com