On 01-07-20, 10:07, Ionela Voinescu wrote: > In the majority of cases, the index argument to cpufreq's target_index() > is meant to identify the frequency that is requested from the hardware, > according to the frequency table: policy->freq_table[index].frequency. > > After successfully requesting it from the hardware, this value, together > with the maximum hardware frequency (policy->cpuinfo.max_freq) are used > as arguments to arch_set_freq_scale(), in order to set the task scheduler > frequency scale factor. This is a normalized indication of a CPU's > current performance. > > But for the vexpress-spc-cpufreq driver, when big.LITTLE switching [1] > is enabled, there are three issues with using the above information for > setting the FI scale factor: > > - cur_freq: policy->freq_table[index].frequency is not the frequency > requested from the hardware. ve_spc_cpufreq_set_rate() will convert > from this virtual frequency to an actual frequency, which is then > requested from the hardware. For the A7 cluster, the virtual frequency > is half the actual frequency. The use of the virtual policy->freq_table > frequency results in an incorrect FI scale factor. > > - max_freq: policy->cpuinfo.max_freq does not correctly identify the > maximum frequency of the physical cluster. This value identifies the > maximum frequency achievable by the big-LITTLE pair, that is the > maximum frequency of the big CPU. But when the LITTLE CPU in the group > is used, the hardware maximum frquency passed to arch_set_freq_scale() > is incorrect. > > - missing a scale factor update: when switching clusters, the driver > recalculates the frequency of the old clock domain based on the > requests of the remaining CPUs in the domain and asks for a clock > change. But this does not result in an update in the scale factor. > > Therefore, introduce a local function bLs_set_sched_freq_scale() that > helps call arch_set_freq_scale() with correct information for the > is_bL_switching_enabled() case, while maintaining the old, more > efficient, call site of arch_set_freq_scale() for when cluster > switching is disabled. > > Also, because of these requirements in computing the scale factor, this > driver is the only one that maintains custom support for FI, which is > marked by the presence of the CPUFREQ_CUSTOM_SET_FREQ_SCALE flag. > > [1] https://lwn.net/Articles/481055/ > > Signed-off-by: Ionela Voinescu <[email protected]> > Cc: Viresh Kumar <[email protected]> > Cc: Sudeep Holla <[email protected]> > Cc: Rafael J. Wysocki <[email protected]> > Cc: Liviu Dudau <[email protected]> > --- > drivers/cpufreq/vexpress-spc-cpufreq.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-)
Is there anyone who cares for this driver and EAS ? I will just skip doing the FIE thing here and mark it skipped. -- viresh
