On Tuesday, October 26, 2010, Arjan van de Ven wrote: > On 10/26/2010 1:38 PM, Rafael J. Wysocki wrote: > > On Tuesday, October 26, 2010, Pierre Tardy wrote: > >> On Tue, Oct 26, 2010 at 2:08 PM, Rafael J. Wysocki<rjw@xxxxxxx> wrote: > >>> On Tuesday, October 26, 2010, Pierre Tardy wrote: > >>>> On Tue, Oct 26, 2010 at 12:58 PM, Peter Zijlstra<peterz@xxxxxxxxxxxxx> wrote: > >>>>> On Tue, 2010-10-26 at 11:56 -0500, Pierre Tardy wrote: > >>>>>> + trace_runtime_pm_usage(dev, atomic_read(&dev->power.usage_count)+1); > >>>>>> atomic_inc(&dev->power.usage_count); > >>>>> That's terribly racy.. > >>>>> > >>>> I know. I'm not proud of this.. As I said, this is preliminary patch. > >>>> We dont really need to have this prev_usage. This is just for debug. > >>>> It mayprobably endup with something like: > >>>> > >>>> atomic_inc(&dev->power.usage_count); > >>>> + trace_power_device_usage(dev); > >>> Well, please tell me what you're trying to achieve. > >> Please see attached the kind of pytimechart output I'm trying to > >> achieve (yes, this chart is not coherent, seems I'm still missing some > >> traces) > >> > >> We basically want to have a trace point eachtime the usage_counter > >> changes, so that I can display nice timecharts, and Arjan can have the > >> comm of the process that eventually generated the rpm_get, in order to > >> pinpoint it in powertop. > >> > >> What you dont see in the above two lines is that > >> trace_power_device_usage(dev); actually reads the usage_count, as well > >> as the driver and device name. > > I'm afraid that for this to really work you'd need to put usage_count under a > > spinlock along with your trace point, which I'm not really sure I like. > > > > Besides, I'm not really sure the manipulations of usage_count are worth > > tracing. > > what's most interesting is the 0->1 and 1->0 transitions. But they are only meaningful in specific situations. For example, if someone does pm_runtime_get_noresume() when the device is active, there may be a device suspend already under way at the same time. So IMO what really is interesting is when rpm_resume() is called with usage_count > 0 and then perhaps when rpm_idle() or rpm_suspend() is called after usage_count drops back to 0. There are some other interesting cases, but they all need to be checked under ->power.lock and you need to do that cleverly, so that the _functionality_ is not harmed. Overall, I think that adding tracepoints to the runtime PM core code is really premature at this point, given that we've just reworked it quite a bit recently. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-trace-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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