| Message ID | 2233690.N3OVLkotou@kreacher |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] cpufreq: Introduce target min and max frequency hints | expand |
Hi Rafael: Thank you for this patch set. I can not get the patch to apply. I was trying on top on 5.10-rc2, and have been unable to determine what other patches might need to be applied first. On 2020.11.05 10:24 Rafael J. Wysocki wrote: ... > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > drivers/cpufreq/cpufreq.c | 3 +++ > drivers/cpufreq/cpufreq_performance.c | 4 ++++ > drivers/cpufreq/cpufreq_powersave.c | 4 ++++ > include/linux/cpufreq.h | 16 ++++++++++++++++ I do not understand why this part says to look for 16 differences, but I can only find 2. > 4 files changed, 27 insertions(+) > > Index: linux-pm/include/linux/cpufreq.h > =================================================================== > --- linux-pm.orig/include/linux/cpufreq.h > +++ linux-pm/include/linux/cpufreq.h > @@ -63,6 +63,8 @@ struct cpufreq_policy { > > unsigned int min; /* in kHz */ > unsigned int max; /* in kHz */ > + unsigned int target_min; /* in kHz */ > + unsigned int target_max; /* in kHz */ > unsigned int cur; /* in kHz, only needed if cpufreq > * governors are used */ > unsigned int suspend_freq; /* freq to set during suspend */ > Index: linux-pm/drivers/cpufreq/cpufreq.c ... Anyway, I edited the patch, deleting the include/linux/cpufreq.h part, then it applied, as did patch 2 of 2. I edited include/linux/cpufreq.h manually. Issues with the powersave governor reported in [1] and [2] are fixed. Relevant part quoted and updated below: > In early September Doug wrote: >> powersave governor: >> acpi-cpufreq: good >> intel_cpufreq hwp: bad Now good, with this patch set. >> intel_cpufreq no hwp: good ... > For the powersave governor, this is what we have now: > > intel_cpufreq hwp == intel_pstate hwp > intel_cpufreq no hwp == acpi-cpufreq == always minimum freq > intel_pstate no hwp ~= acpi-cpufreq/ondemand ... > My expectation was/is: > > intel_cpufreq hwp == intel_cpufreq no hwp == acpi-cpufreq == always minimum freq And this is what we now have, with this patch set. > intel_pstate no hwp ~= acpi-cpufreq/ondemand > intel_pstate hwp == Unique. Say, extremely course version of ondemand. [1] https://marc.info/?l=linux-pm&m=159769839401767&w=2 [2] https://marc.info/?l=linux-pm&m=159943780220923&w=2 ... Doug
On 05-11-20, 19:23, Rafael J. Wysocki wrote: > Index: linux-pm/include/linux/cpufreq.h > =================================================================== > --- linux-pm.orig/include/linux/cpufreq.h > +++ linux-pm/include/linux/cpufreq.h > @@ -63,6 +63,8 @@ struct cpufreq_policy { > > unsigned int min; /* in kHz */ > unsigned int max; /* in kHz */ > + unsigned int target_min; /* in kHz */ > + unsigned int target_max; /* in kHz */ > unsigned int cur; /* in kHz, only needed if cpufreq > * governors are used */ > unsigned int suspend_freq; /* freq to set during suspend */ Rafael, honestly speaking I didn't like this patch very much. We need to fix a very specific problem with the intel-pstate driver when it is used with powersave/performance governor to make sure the hard limits are enforced. And this is something which no one else may face as well. What about doing something like this instead in the intel_pstate driver only to get this fixed ? if (!strcmp(policy->governor->name, "powersave") || !strcmp(policy->governor->name, "performance")) hard-limit-to-be-enforced; This would be a much simpler and contained approach IMHO. -- viresh
On Fri, Nov 6, 2020 at 11:07 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 05-11-20, 19:23, Rafael J. Wysocki wrote: > > Index: linux-pm/include/linux/cpufreq.h > > =================================================================== > > --- linux-pm.orig/include/linux/cpufreq.h > > +++ linux-pm/include/linux/cpufreq.h > > @@ -63,6 +63,8 @@ struct cpufreq_policy { > > > > unsigned int min; /* in kHz */ > > unsigned int max; /* in kHz */ > > + unsigned int target_min; /* in kHz */ > > + unsigned int target_max; /* in kHz */ > > unsigned int cur; /* in kHz, only needed if cpufreq > > * governors are used */ > > unsigned int suspend_freq; /* freq to set during suspend */ > > Rafael, honestly speaking I didn't like this patch very much. So what's the concern, specifically? > We need to fix a very specific problem with the intel-pstate driver when it is > used with powersave/performance governor to make sure the hard limits > are enforced. And this is something which no one else may face as > well. Well, I predict that the CPPC driver will face this problem too at one point. As well as any other driver which doesn't select OPPs directly for that matter, at least to some extent (note that intel_pstate in the "passive" mode without HWP has it too, but since there is no way to enforce the target max in that case, it is not relevant). > What about doing something like this instead in the intel_pstate > driver only to get this fixed ? > > if (!strcmp(policy->governor->name, "powersave") || > !strcmp(policy->governor->name, "performance")) > hard-limit-to-be-enforced; > > This would be a much simpler and contained approach IMHO. I obviously prefer to do it the way I did in this series, because it is more general and it is based on the governor telling the driver what is needed instead of the driver trying to figure out what the governor is and guessing what may be needed because of that. But if you have a very specific technical concern regarding my approach, I can do it the other way too. Cheers!
On 06-11-20, 18:02, Rafael J. Wysocki wrote: > On Fri, Nov 6, 2020 at 11:07 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > > > On 05-11-20, 19:23, Rafael J. Wysocki wrote: > > > Index: linux-pm/include/linux/cpufreq.h > > > =================================================================== > > > --- linux-pm.orig/include/linux/cpufreq.h > > > +++ linux-pm/include/linux/cpufreq.h > > > @@ -63,6 +63,8 @@ struct cpufreq_policy { > > > > > > unsigned int min; /* in kHz */ > > > unsigned int max; /* in kHz */ > > > + unsigned int target_min; /* in kHz */ > > > + unsigned int target_max; /* in kHz */ > > > unsigned int cur; /* in kHz, only needed if cpufreq > > > * governors are used */ > > > unsigned int suspend_freq; /* freq to set during suspend */ > > > > Rafael, honestly speaking I didn't like this patch very much. > > So what's the concern, specifically? > > > We need to fix a very specific problem with the intel-pstate driver when it is > > used with powersave/performance governor to make sure the hard limits > > are enforced. And this is something which no one else may face as > > well. > > Well, I predict that the CPPC driver will face this problem too at one point. > > As well as any other driver which doesn't select OPPs directly for > that matter, at least to some extent (note that intel_pstate in the > "passive" mode without HWP has it too, but since there is no way to > enforce the target max in that case, it is not relevant). > > > What about doing something like this instead in the intel_pstate > > driver only to get this fixed ? > > > > if (!strcmp(policy->governor->name, "powersave") || > > !strcmp(policy->governor->name, "performance")) > > hard-limit-to-be-enforced; > > > > This would be a much simpler and contained approach IMHO. > > I obviously prefer to do it the way I did in this series, because it > is more general and it is based on the governor telling the driver > what is needed instead of the driver trying to figure out what the > governor is and guessing what may be needed because of that. > > But if you have a very specific technical concern regarding my > approach, I can do it the other way too. I was concerned about adding those fields in the policy structure, but I get that you want to do it in a more generic way. What about adding a field name "fixed" (or something else) in the governor's structure which tells us that the frequency is fixed and must be honored by the driver. -- viresh
On Mon, Nov 9, 2020 at 5:39 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > On 06-11-20, 18:02, Rafael J. Wysocki wrote: > > On Fri, Nov 6, 2020 at 11:07 AM Viresh Kumar <viresh.kumar@linaro.org> wrote: > > > > > > On 05-11-20, 19:23, Rafael J. Wysocki wrote: > > > > Index: linux-pm/include/linux/cpufreq.h > > > > =================================================================== > > > > --- linux-pm.orig/include/linux/cpufreq.h > > > > +++ linux-pm/include/linux/cpufreq.h > > > > @@ -63,6 +63,8 @@ struct cpufreq_policy { > > > > > > > > unsigned int min; /* in kHz */ > > > > unsigned int max; /* in kHz */ > > > > + unsigned int target_min; /* in kHz */ > > > > + unsigned int target_max; /* in kHz */ > > > > unsigned int cur; /* in kHz, only needed if cpufreq > > > > * governors are used */ > > > > unsigned int suspend_freq; /* freq to set during suspend */ > > > > > > Rafael, honestly speaking I didn't like this patch very much. > > > > So what's the concern, specifically? > > > > > We need to fix a very specific problem with the intel-pstate driver when it is > > > used with powersave/performance governor to make sure the hard limits > > > are enforced. And this is something which no one else may face as > > > well. > > > > Well, I predict that the CPPC driver will face this problem too at one point. > > > > As well as any other driver which doesn't select OPPs directly for > > that matter, at least to some extent (note that intel_pstate in the > > "passive" mode without HWP has it too, but since there is no way to > > enforce the target max in that case, it is not relevant). > > > > > What about doing something like this instead in the intel_pstate > > > driver only to get this fixed ? > > > > > > if (!strcmp(policy->governor->name, "powersave") || > > > !strcmp(policy->governor->name, "performance")) > > > hard-limit-to-be-enforced; > > > > > > This would be a much simpler and contained approach IMHO. > > > > I obviously prefer to do it the way I did in this series, because it > > is more general and it is based on the governor telling the driver > > what is needed instead of the driver trying to figure out what the > > governor is and guessing what may be needed because of that. > > > > But if you have a very specific technical concern regarding my > > approach, I can do it the other way too. > > I was concerned about adding those fields in the policy structure, but > I get that you want to do it in a more generic way. > > What about adding a field name "fixed" (or something else) in the > governor's structure which tells us that the frequency is fixed and > must be honored by the driver. That would work for powersave/performance and it would suffice for the time being, so let me try to implement that. Still, there is a more general problem related to that which is how to prevent the perf control in the hardware from going beyond certain limits, possibly narrower than the policy min and max. For example, the kernel may need to reserve some capacity for deadline tasks or similar, or when there is a min utilization clamp in place, and it would be good to have a way to let the HW know that it should not reduce the available capacity below a certain boundary, even though that may appear to be the right thing to do to it. [This is kind of addressed by intel_pstate by setting the HWP floor to the target frequency requested by the governor, but that is suboptimal, because it generally causes too much capacity to be reserved which costs energy.] Analogously, the kernel may not want the HW to increase capacity too much when it knows that doing so would not increase the amount of work done or when the work being done is not urgent (like when there is a max utilization clamp in place), [This last issue is particularly visible in some GPU-related workloads where the processor sees conditions for ramping up a "one-core turbo" frequency very high, but this is a mistake, because it doesn't cause work to be done any faster, since the task doing the work is in fact periodic and it does the same amount of work in every period regardless of how fast the CPU doing it runs.] So while the powersave/performance case can be addressed in a simpler way, the need for a more general approach is still there.
Index: linux-pm/include/linux/cpufreq.h =================================================================== --- linux-pm.orig/include/linux/cpufreq.h +++ linux-pm/include/linux/cpufreq.h @@ -63,6 +63,8 @@ struct cpufreq_policy { unsigned int min; /* in kHz */ unsigned int max; /* in kHz */ + unsigned int target_min; /* in kHz */ + unsigned int target_max; /* in kHz */ unsigned int cur; /* in kHz, only needed if cpufreq * governors are used */ unsigned int suspend_freq; /* freq to set during suspend */ Index: linux-pm/drivers/cpufreq/cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq.c +++ linux-pm/drivers/cpufreq/cpufreq.c @@ -2272,6 +2272,9 @@ static int cpufreq_init_governor(struct pr_debug("%s: for CPU %u\n", __func__, policy->cpu); + policy->target_min = policy->cpuinfo.min_freq; + policy->target_max = policy->cpuinfo.max_freq; + if (policy->governor->init) { ret = policy->governor->init(policy); if (ret) { Index: linux-pm/drivers/cpufreq/cpufreq_performance.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq_performance.c +++ linux-pm/drivers/cpufreq/cpufreq_performance.c @@ -14,6 +14,10 @@ static void cpufreq_gov_performance_limits(struct cpufreq_policy *policy) { pr_debug("setting to %u kHz\n", policy->max); + + policy->target_min = policy->max; + policy->target_max = policy->max; + __cpufreq_driver_target(policy, policy->max, CPUFREQ_RELATION_H); } Index: linux-pm/drivers/cpufreq/cpufreq_powersave.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq_powersave.c +++ linux-pm/drivers/cpufreq/cpufreq_powersave.c @@ -14,6 +14,10 @@ static void cpufreq_gov_powersave_limits(struct cpufreq_policy *policy) { pr_debug("setting to %u kHz\n", policy->min); + + policy->target_min = policy->min; + policy->target_max = policy->min; + __cpufreq_driver_target(policy, policy->min, CPUFREQ_RELATION_L); }