Messages in this thread | | | Date | Fri, 4 Mar 2016 00:18:11 +0800 | From | Huang Rui <> | Subject | Re: [PATCH v6 2/2] perf/x86/amd/power: Add AMD accumulated power reporting mechanism |
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On Thu, Mar 03, 2016 at 04:26:46PM +0100, Thomas Gleixner wrote: > On Thu, 3 Mar 2016, Huang Rui wrote: > > On Thu, Mar 03, 2016 at 09:50:11AM +0100, Thomas Gleixner wrote: > > > On Thu, 3 Mar 2016, Huang Rui wrote: > > > And of course if CPU_DOWN_PREPARE fails and this is the last cpu in the > > > compute unit, nothing takes over the duty for this compute unit. So you need > > > to handle CPU_DOWN_FAILED .... > > > > > > > OK, so I need to do power_cpu_init when notified CPU_DOWN_FAILED, am I > > right? > > Yes. > > > > > + cpu_notifier_register_begin(); > > > > + > > > > + /* Choose one online core of each compute unit. */ > > > > + for (i = 0; i < boot_cpu_data.x86_max_cores; i += smp_num_siblings) { > > > > + WARN_ON(cpumask_empty(topology_sibling_cpumask(i))); > > > > > > Err. What guarantees that in each compute unit is one sibling online? And what > > > value has that WARN_ON? We don't care about the stack trace here, because it's > > > known already. > > > > > > > When this driver is not as module before, I think there should be one > > sibling online at least at initialization phase. But now, you're > > right, we cannot guarantee it. > > > > > > + cpumask_set_cpu(cpumask_any(topology_sibling_cpumask(i)), &cpu_mask); > > > > > > Of course you just continue in that case and end up with: > > > > > > cpumask_set_cpu(nr_cpu_ids, &cpu_mask); > > > > > > i.e. you try to do that on an invalid bit, which will trigger a justified > > > warning in cpumask_set_cpu() if CONFIG_DEBUG_PER_CPU_MAPS is enabled. > > > > > > Aside of that this only handles a single socket. And why do you do the above > > > if you handle the same thing in the loop below? > > > > > > > Because the sibling online shouldn't be empty at initialization phase > > if the driver is not module before. So... > > > > Thanks to catch it. > > > > How about below update: > > > > for (i = 0; i < boot_cpu_data.x86_max_cores; i += smp_num_siblings) { > > if (!cpumask_empty(topology_sibling_cpumask(i))) > > cpumask_set_cpu(cpumask_any(topology_sibling_cpumask(i)), &cpu_mask); > > } > > Why? You do a full for_each_online_cpu(i) loop after that, which does > exactly the same thing, right? >
But looks like power_cpu_init cannot handle it if we don't take any action here.
e. g. cpu_mask: 0000 and online mask: 1111 -> power_cpu_init(0) -> cpu_mask is still: 0000
topology_sibling_cpumask(0): 0011 target: 1 (i. e. we cannot do cpumask_set_cpu(0, &cpu_mask))
Maybe, we need to think out a stronger power_cpu_init if you want to only do init thing at for_each_online_cpu.
> > > > + } > > > > + > > > > + for_each_online_cpu(i) > > > > + power_cpu_init(i); > > > > + > > > > + __register_cpu_notifier(&power_cpu_notifier_nb); > > > > + > > > > + ret = perf_pmu_register(&pmu_class, "power", -1); > > > > + if (WARN_ON(ret)) { > > > > + pr_warn("AMD Power PMU registration failed\n"); > > > > > > This still leaks the cpu notifier. ..... > > > > > > > OK, so I should do __unregister_cpu_notifier(&power_cpu_notifier_nb) > > here. > > You can register the notifier after perf_pmu_register succeeded, right? >
Yep.
> > > > + pr_info("AMD Power PMU detected, %d compute units\n", cu_num); > > > > > > Why is the number of compute units interesting at all? > > > > > > > Because the accumulated power bases on compute units. > > We can see the mask from /sys/devices/power/cpumask and number of > > compute units to know if all compute units are set at cpumask. > > So I add a printk here, does it make sense? > > No, because it's completely non intuitive. How on earth am I supposed to get > the connection between /sys/devices/power/cpumask and number of compute units > without staring at the code? So this is only interesting for a developer who > can deduce that number from /proc/cpuinfo or dmesg as well. >
OK, I will remove unnecessary cu_num next version.
Thanks, Rui
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