On 5/3/2018 2:32 AM, Rafael J. Wysocki wrote: > On Wed, May 2, 2018 at 5:39 PM, Prakash, Prashanth > <pprakash@xxxxxxxxxxxxxx> wrote: >> Hi Viresh, >> >> >> On 4/27/2018 11:35 AM, Prashanth Prakash wrote: >>> Add support to specify platform specific transition_delay_us instead >>> of using the transition delay derived from PCC. >>> >>> With commit "3d41386d556d: cpufreq: CPPC: Use transition_delay_us >>> depending transition_latency" we are setting transition_delay_us >>> directly and not applying the LATENCY_MULTIPLIER. With this on Qualcomm >>> Centriq we can end up with a very high rate of frequency change requests >>> when using schedutil governor (default rate_limit_us=10 compared to an >>> earlier value of 10000). >>> >>> The PCC subspace describes the rate at which the platform can accept >>> commands on the CPPC's PCC channel. This includes read and write >>> command on the PCC channel that can be used for reasons other than >>> frequency transitions. Moreover the same PCC subspace can be used by >>> multiple freq domains and deriving transition_delay_us from it as we do >>> now can be sub-optimal. >>> >>> Moreover if a platform does not use PCC for desired_perf register then >>> there is no way to compute the transition latency or the delay_us. >>> >>> CPPC does not have a standard defined mechanism to get the transition >>> rate or the latency at the moment. >>> >>> Given the above limitations, it is simpler to have a platform specific >>> transition_delay_us and rely on PCC derived value only if a platform >>> specific value is not available. >>> >>> Signed-off-by: Prashanth Prakash <pprakash@xxxxxxxxxxxxxx> >>> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx> >>> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> >>> Cc: 4.14+ <stable@xxxxxxxxxxxxxxx> >>> Fixes: 3d41386d556d ("cpufreq: CPPC: Use transition_delay_us depending >>> transition_latency) >>> --- >>> v2: >>> * Return final delay_us from cppc_cpufreq_get_transition_delay_us (Viresh) >>> v3 and v4: >>> * code style changes (Viresh) >>> --- >>> drivers/cpufreq/cppc_cpufreq.c | 47 ++++++++++++++++++++++++++++++++++++++++-- >>> 1 file changed, 45 insertions(+), 2 deletions(-) >> Any inputs on this patch? I was hoping to get this in for 4.17 as it fixes undesirable(very low) >> transition delay when using schedutil governor on centriq platform. > I've queued it up for -rc4. I have a plan to push it later today. Thanks Viresh and Rafael! -Prashanth