On Fri, 23 Apr 2010 14:40:42 -0400 Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > [CCing Arjan, who seems to have played a lot with ondemand lately] > > * Saravana Kannan (skannan@xxxxxxxxxxxxxx) wrote: > > Resending email to "cc" the maintainers. > > > > Maintainers, > > > > Any comments? > > > > -Saravana > > > > Saravana Kannan wrote: > >> Hi, > >> > >> I think there are a couple of issues with cpufreq and udelay > >> interaction. But that's based on my understanding of cpufreq. I > >> have worked with it for sometime now, so hopefully I not > >> completely wrong. So, I will list my assumptions and what I think > >> is/are the issue(s) and their solutions. > >> > >> Please correct me if I'm wrong and let me know what you think. > >> > >> Assumptions: > >> ============ > >> * Let's assume ondemand governor is being used. > >> * Ondemand uses one timer per core and they have CPU affinity set. > >> * For SMP, CPUfreq core expects the CPUfreq driver to adjust the > >> per-CPU jiffies. > >> * P1 indicates for lower CPU perfomance levels and P2 indicates a > >> much higher CPU pref level (say 10 times faster). > >> so in reality, all hardware that does coordination between cores/etc like this also has a tsc that is invariant of the actual P state. If there are exceptions, those have a problem, but I can't think of any right now. Once the TSC is invariant of P state, udelay() is fine, since that goes of the tsc, not of some delay loop kind of thing.... -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
