Messages in this thread | | | Date | Wed, 29 May 2019 10:41:18 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC 3/3] preempt_tracer: Use a percpu variable to control traceble calls |
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On Tue, May 28, 2019 at 05:16:24PM +0200, Daniel Bristot de Oliveira wrote: > #if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \ > defined(CONFIG_TRACE_PREEMPT_TOGGLE)) > + > +DEFINE_PER_CPU(int, __traced_preempt_count) = 0; > /* > * If the value passed in is equal to the current preempt count > * then we just disabled preemption. Start timing the latency. > */ > void preempt_latency_start(int val) > { > - if (preempt_count() == val) { > + int curr = this_cpu_read(__traced_preempt_count);
We actually have this_cpu_add_return();
> + > + if (!curr) { > unsigned long ip = get_lock_parent_ip(); > #ifdef CONFIG_DEBUG_PREEMPT > current->preempt_disable_ip = ip; > #endif > trace_preempt_off(CALLER_ADDR0, ip); > } > + > + this_cpu_write(__traced_preempt_count, curr + val); > } > > static inline void preempt_add_start_latency(int val) > @@ -3200,8 +3206,12 @@ NOKPROBE_SYMBOL(preempt_count_add); > */ > void preempt_latency_stop(int val) > { > - if (preempt_count() == val) > + int curr = this_cpu_read(__traced_preempt_count) - val;
this_cpu_sub_return();
> + > + if (!curr) > trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip()); > + > + this_cpu_write(__traced_preempt_count, curr); > }
Can't say I love this, but it is miles better than the last patch.
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