Messages in this thread | | | Date | Fri, 7 Feb 2014 18:08:45 +0100 | From | Torsten Duwe <> | Subject | Re: [PATCH] Convert powerpc simple spinlocks into ticket locks |
| |
On Fri, Feb 07, 2014 at 04:18:47PM +0100, Peter Zijlstra wrote: > On Fri, Feb 07, 2014 at 01:28:37PM +0100, Peter Zijlstra wrote: > > Anyway, you can do a version with lwarx/stwcx if you're looking get rid > > of lharx. > > the below seems to compile into relatively ok asm. It can be done better > if you write the entire thing by hand though.
[...]
> > static inline unsigned int xadd(unsigned int *v, unsigned int i) > { > int t, ret; > > __asm__ __volatile__ ( > "1: lwarx %0, 0, %4\n" > " mr %1, %0\n" > " add %0, %3, %0\n" > " stwcx. %0, %0, %4\n" > " bne- 1b\n" > : "=&r" (t), "=&r" (ret), "+m" (*v) > : "r" (i), "r" (v) > : "cc"); > > return ret; > } > I don't like this xadd thing -- it's so x86 ;) x86 has its LOCK prefix, ppc has ll/sc. That should be reflected somehow IMHO.
Maybe if xadd became mandatory for some kernel library.
> > void ticket_unlock(tickets_t *lock) > { > ticket_t tail = lock->tail + 1; > > /* > * The store is save against the xadd for it will make the ll/sc fail > * and try again. Aside from that PowerISA guarantees single-copy > * atomicy for half-word writes. > * > * And since only the lock owner will ever write the tail, we're good. > */ > smp_store_release(&lock->tail, tail); > }
Yeah, let's try that on top of v2 (just posted). First, I want to see v2 work as nicely as v1 -- compiling a debug kernel takes a while...
Torsten
| |