On Fri, 7 Apr 2017 07:43:35 -0700 "Paul E. McKenney" <[email protected]> wrote:
> On Fri, Apr 07, 2017 at 10:01:06AM -0400, Steven Rostedt wrote: > > Paul, > > > > Here's my latest. You OK with it? > > Given your update to 3/5, I suspect that we could live with it. I am > expecting some complaints about increases in idle-entry latency, but might > be best to wait for complaints rather than complexifying too proactively. We only added a this_cpu_inc() and this_cpu_dec() which are very fast operations. I highly doubt it will be measurable. Although, I'm talking about x86, IIRC, the this_cpu_inc/dec were be poorly written for other archs in the past. I'm not sure if that was fixed though. > > That said, there isn't supposed to be any tracing during the now very > small interval where RCU's idle-entry is incomplete. Mightn't it be > better to (under CONFIG_PROVE_RCU or some such) give splats if tracing > showed up in that interval? > Again, tracing is not the issue. I do function tracing in that location without any problems. The issue here was the stack tracer. Maybe we can create a new variable that is more cache local to the RCU code. What about calling it "rcu_disabled"? Then tracing that depends on RCU can simply check that. s/stack_trace_disable/disable_rcu/ s/stack_trace_enable/enable_rcu/ export a per cpu variable rcu_disabled Then I can have the stack tracer check that variable as well. And we could even put in a WARN_ON(this_cpu_read(rcu_disabled) in the TRACE_EVENT() macros. Thoughts? -- Steve
