Messages in this thread | | | From | Vineet Gupta <> | Subject | Re: [RFC] perf: fix building for ARCv1 | Date | Tue, 20 Oct 2015 10:45:25 +0000 |
| |
On Tuesday 20 October 2015 03:41 PM, Peter Zijlstra wrote: >> > Can we use existing syscall(s) - again this is what our good old pthread library >> > code did. >> > >> > static void __pthread_acquire(int * spinlock) >> > { >> > int cnt = 0; >> > struct timespec tm; >> > >> > READ_MEMORY_BARRIER(); >> > >> > while (testandset(spinlock)) { <---- atomic EXchange >> > if (cnt < 50) { >> > sched_yield(); >> > cnt++; >> > } else { >> > tm.tv_sec = 0; >> > tm.tv_nsec = 2000001; >> > nanosleep(&tm, ((void *)0)); >> > cnt = 0; >> > } >> > } > *shudder* that is quite horrible. > > This means all your 'atomics' are broken for anything SCHED_FIFO and the > like. You simply _cannot_ run a realtime system.
The code above is from uClibc old threading library which we don't use anymore. The NPTL version doesn't have all of this song-n-dance and relies on futexes. The change we are talking about is only for the atomics in perf itself. I do understand your POV though.
> (also, for ACQUIRE you want the READ_MEMORY_BARRIER() _after_ the > test-and-set control dependency.)
Absolutely and in this case it will have to be added both inside the loop and one at the end to cover both the scenarios !
| |