Messages in this thread | | | Date | Fri, 16 Mar 2012 08:23:41 +0900 | From | Simon Horman <> | Subject | Re: [PATCH] regulator: notify sysfs when voltage is set |
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On Thu, Mar 15, 2012 at 02:47:08PM +0000, Mark Brown wrote: > On Thu, Mar 15, 2012 at 11:26:58PM +0900, Simon Horman wrote: > > On Thu, Mar 15, 2012 at 12:46:31PM +0000, Mark Brown wrote: > > > > I notice that we don't generate similar events for cpufreq... what are > > > the performance implications from firing off udev (which isn't free) > > > every time we scale the CPU frequency? It feels like this might be > > > disruptive, especially with a governor like ondemand which responds to > > > system load. > > > that is a good point and to be honest not one that I had considered. For > > the use-case that I have in mind, which is basically to log voltage changes > > over time, it may be acceptable to rate-limit notifications somehow. But at > > that point I may be better off just polling. > > Hrm, if you're doing logging then we do already have tracepoints defined > for voltage changes - could you have your application work with those > instead of sysfs? One of the applications of tracepoints is flight > recorder style system monitoring.
Thanks, that does sound like it would work for me. I'll look into it further.
> > Out of interest, how often can ondemand potentially change the voltage? > > Depends on how slow it thinks frequency changes are. I'm not so worried > about the performance impact from that point of view, I'm more worried > about what happens when we lower the clock frequency and generate a > sysfs event causing userspace to wake up and start doing stuff. It'd be > bad if ondemand (or another dynamic governor) noticed that the system > got more busy again and responded by ramping the frequency...
Ok, understood, that could be a bit nasty.
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