Messages in this thread | | | Date | Thu, 6 Feb 2014 18:37:27 +0100 | From | Torsten Duwe <> | Subject | Re: [PATCH] Convert powerpc simple spinlocks into ticket locks |
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On Thu, Feb 06, 2014 at 05:38:37PM +0100, Peter Zijlstra wrote: > On Thu, Feb 06, 2014 at 11:37:37AM +0100, Torsten Duwe wrote: > > x86 has them, MIPS has them, ARM has them, even ia64 has them: > > ticket locks. They reduce memory bus and cache pressure especially > > for contended spinlocks, increasing performance. > > > > This patch is a port of the x86 spin locks, mostly written in C, > > to the powerpc, introducing inline asm where needed. The pSeries > > directed yield for vCPUs is taken care of by an additional "holder" > > field in the lock. > > > > A few questions; what's with the ppc64 holder thing? Not having a 32bit > spinlock_t is sad.
I must admit that I haven't tested the patch on non-pseries ppc64 nor on ppc32. Only ppc64 has the ldarx and I tried to atomically replace the holder along with the locks. That might prove unneccessary.
> Can you pair lwarx with sthcx ? I couldn't immediately find the answer > in the PowerISA doc. If so I think you can do better by being able to > atomically load both tickets but only storing the head without affecting > the tail.
V2.06b, Book II, Chapter 3, "sthcx" says: | If a reservation exists and the length associated [...] is not 2 bytes, | it is undefined whether (RS)_48:63 are stored [...]
That doesn't make me feel comfortable :(
Torsten
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