Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1251574

Re: [RFC] perf: fix building for ARCv1

Show all headers | View raw

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 !

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [RFC] perf: fix building for ARCv1 Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2015-10-18 13:20 +0200
  Re: [RFC] perf: fix building for ARCv1 Andi Kleen <andi@firstfloor.org> - 2015-10-19 01:20 +0200
    Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-19 07:00 +0200
      Re: [RFC] perf: fix building for ARCv1 Andi Kleen <andi@firstfloor.org> - 2015-10-19 08:00 +0200
        Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-19 11:30 +0200
          Re: [RFC] perf: fix building for ARCv1 Peter Zijlstra <peterz@infradead.org> - 2015-10-19 11:40 +0200
            Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-19 11:50 +0200
              Re: [RFC] perf: fix building for ARCv1 Peter Zijlstra <peterz@infradead.org> - 2015-10-19 12:00 +0200
                Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-19 12:10 +0200
                Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-20 10:10 +0200
                Re: [RFC] perf: fix building for ARCv1 Peter Zijlstra <peterz@infradead.org> - 2015-10-20 12:20 +0200
                Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-20 12:50 +0200
                Re: [RFC] perf: fix building for ARCv1 Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2015-10-29 17:00 +0100
                Re: [RFC] perf: fix building for ARCv1 Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-10-30 07:30 +0100

csiph-web