On Mon, 24 Apr 2017 10:51:54 +0200 Peter Zijlstra <pet...@infradead.org> wrote:
> On Fri, Apr 21, 2017 at 10:49:29PM -0400, Steven Rostedt wrote: > > When a CPU schedules in a lower priority task and wants to make sure > > overloaded CPUs know about it. It increments the rto_loop_next. Then it does > > an atomic_inc_return() on rto_loop_start. If the returned value is not "1", > > then it does atomic_dec() on rt_loop_start and returns. If the value is "1", > > then it will take the rto_lock to synchronize with a possible IPI being sent > > around to the overloaded CPUs. > > > + start = atomic_inc_return(&rq->rd->rto_loop_start); > > + if (start != 1) > > + goto out; > > > +out: > > + atomic_dec(&rq->rd->rto_loop_start); > > > Did you just write a very expensive test-and-set trylock? Probably. I didn't know we had a generic one. Where is it? $ git grep test_and_set |grep trylock fs/jfs/jfs_metapage.c:#define trylock_metapage(mp) test_and_set_bit_lock(META_locked, &(mp)->flag) I don't think the above is what you mean. -- Steve
