On Tue, Apr 24, 2018 at 11:23:02AM -0700, Paul E. McKenney wrote: > On Tue, Apr 24, 2018 at 10:26:58AM -0700, Paul E. McKenney wrote: > > On Tue, Apr 24, 2018 at 09:01:34AM -0700, Joel Fernandes wrote: > > > On Tue, Apr 24, 2018 at 8:56 AM, Paul E. McKenney > > > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > On Mon, Apr 23, 2018 at 05:22:44PM -0400, Steven Rostedt wrote: > > > >> On Mon, 23 Apr 2018 13:12:21 -0400 (EDT) > > > >> Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > > > >> > > > >> > > > >> > I'm inclined to explicitly declare the tracepoints with their given > > > >> > synchronization method. Tracepoint probe callback functions for currently > > > >> > existing tracepoints expect to have preemption disabled when invoked. > > > >> > This assumption will not be true anymore for srcu-tracepoints. > > > >> > > > >> Actually, why not have a flag attached to the tracepoint_func that > > > >> states if it expects preemption to be enabled or not? If a > > > >> trace_##event##_srcu() is called, then simply disable preemption before > > > >> calling the callbacks for it. That way if a callback is fine for use > > > >> with srcu, then it would require calling > > > >> > > > >> register_trace_##event##_may_sleep(); > > > >> > > > >> Then if someone uses this on a tracepoint where preemption is disabled, > > > >> we simply do not call it. > > > > > > > > One more stupid question... If we are having to trace so much stuff > > > > in the idle loop, are we perhaps grossly overstating the extent of that > > > > "idle" loop? For being called "idle", this code seems quite busy! > > > > > > ;-) > > > The performance hit I am observing is when running a heavy workload, > > > like hackbench or something like that. That's what I am trying to > > > correct. > > > By the way is there any limitation on using SRCU too early during > > > boot? I backported Mathieu's srcu tracepoint patches but the kernel > > > hangs pretty early in the boot. I register lockdep probes in > > > start_kernel. I am hoping that's not why. > > > > > > I could also have just screwed up the backporting... may be for my > > > testing, I will just replace the rcu API with the srcu instead of all > > > of Mathieu's new TRACE_EVENT macros for SRCU, since all I am trying to > > > do right now is measure the performance of my patches with SRCU. > > > > Gah, yes, there is an entry on my capacious todo list on making SRCU > > grace periods work during early boot and mid-boot. Let me see what > > I can do... > > OK, just need to verify that you are OK with call_srcu()'s callbacks > not being invoked until sometime during core_initcall() time. (If you > really do need them to be invoked before that, in theory it is possible, > but in practice it is weird, even for RCU.) Oh, and that early at boot, you will need to use DEFINE_SRCU() or DEFINE_STATIC_SRCU() rather than dynamic allocation and initialization. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
