On Fri, Jan 23, 2015 at 11:23:36AM -0800, Jason Low wrote: > On Fri, 2015-01-23 at 10:25 +0100, Peter Zijlstra wrote: > > On Thu, Jan 22, 2015 at 07:31:53PM -0800, Jason Low wrote: > > > +static void update_gt_cputime(struct thread_group_cputimer *a, struct > > > task_cputime *b) > > > { > > > + if (b->utime > atomic64_read(&a->utime)) > > > + atomic64_set(&a->utime, b->utime); > > > > > > + if (b->stime > atomic64_read(&a->stime)) > > > + atomic64_set(&a->stime, b->stime); > > > > > > + if (b->sum_exec_runtime > atomic64_read(&a->sum_exec_runtime)) > > > + atomic64_set(&a->sum_exec_runtime, b->sum_exec_runtime); > > > } > > > > See something like this is not safe against concurrent adds. > > How about something like: > > u64 a_utime, a_stime, a_sum_exec_runtime; > > retry_utime: > a_utime = atomic64_read(&a->utime); > if (b->utime > a_utime) { > if (atomic64_cmpxchg(&a->utime, a_utime, b->utime) != a_utime) > goto retry_utime; > } > > retry_stime: > a_stime = atomic64_read(&a->stime); > if (b->stime > a_stime) { > if (atomic64_cmpxchg(&a->stime, a_stime, b->stime) != a_stime) > goto retry_stime; > } > > retry_sum_exec_runtime: > a_sum_exec_runtime = atomic64_read(&a->sum_exec_runtime); > if (b->sum_exec_runtime > a_sum_exec_runtime) { > if (atomic64_cmpxchg(&a->sum_exec_runtime, a_sum_exec_runtime, > b->sum_exec_runtime) != a_sum_exec_runtime) > goto retry_sum_exec_runtime; > }
Disgusting, at least use an inline or macro to avoid repeating it :-) Also, does anyone care about performance on 32bit systems? There's a few where atomic64 is abysmal. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/