Messages in this thread | | | Date | Wed, 29 Jul 2015 18:04:56 +0800 | From | Pan Xinhui <> | Subject | Re: [PATCH] cpufreq: Add scaling frequency range support |
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On 2015年07月29日 17:59, Pan Xinhui wrote: > hi, Rafael > thanks for you reply. > > On 2015年07月29日 08:18, Rafael J. Wysocki wrote: >> On Tuesday, July 28, 2015 12:53:33 PM Pan Xinhui wrote: >>> hi, Viresh >>> thanks for your reply :) >>> On 2015年07月28日 12:29, Viresh Kumar wrote: >>>> On 28-07-15, 11:32, Pan Xinhui wrote: >>>>> From: Pan Xinhui <xinhuix.pan@intel.com> >>>>> >>>>> Userspace at most time do cpufreq tests very much inconveniently. >>>>> Currently they have to echo min and max cpu freq separately like below: >>>>> echo 480000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq >>>>> echo 2240000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq >>>>> >>>>> Add scaling_freq_range cpufreq attr to support userspace's demand. >>>>> Therefore it's easier for testers to write readable scripts like below: >>>>> echo 480000-2240000 > >>>>> /sys/devices/system/cpu/cpu0/cpufreq/scaling_freq_range >>>> >>>> I don't think this brings any good change, we already have support for >>>> that with min/max freqs and I don't see how scripts can be less >>>> readable with that. >>>> >>> yes, min/max are supported, however it is inconvenient. sometime it's very easy to cause obscure bugs. >>> For example, some one might write a script like below. >>> echo 480000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq >>> echo 960000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq >>> .....//other works >>> echo 1120000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq >>> echo 2240000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq >>> ...//other works >>> >>> But it did not work when we echo 112000 to min-freq, as the current max freq is smaller than it. >>> It's hard to figure it out in a big script... we have many such scripts. >> >> Fix them, then, pretty please. >> > of course we will fix them. :) > >> And adding this attribute is not going to magically fix them, is it? >> > yes, this patch can not fix them without changing the script. BUT I have another patch which could magically fix them. :) > > These two attribute files are very tricky. they are related with each other. > Not like some other attribute file in other part of kernel, for example, proc/sys/fs/file-max. > As the file-min is always zero. It's very reasonable to only support file-max attribute file. > > The sequence we echoing value to min/max_freq is very important. Maybe we can also assume they have *state*. > Just like a developer writes a buf to a file. he should do in this way below. > fp = fopen(..) > => fwrite(...) > => fclose(...) > > The script I mentioned above did not follow the right sequence. when script wants to set the min higher, we need set the max first to avoid min > max issue... > So max/min_freq have *state*. just like TCP Three-way handshake, SYN, ACK&SYN, ACK. the sequence(this is so-called state) is very important. > > Now I want to offer a non-state attribute to user-space :) > This is a design/engineering problem. It's okay for kernel to not offer such attribute. But user-space will do more work. > For example, In the worst case, we need system call four times. > read min/max_freq (system call two times) > might set min or max freq first to avoid min > max issue (system call one time) > set min/max a new value (system call one time) > > What if we offer *set freq range* attribute? just once. :) > set freq range (system call one time) > > From performance point, It's a good idea to offer such attribute. > > There is another reason for why it's good to apply this patch. > If cpufreg range is 480000-960000, we call it powersave, 480000-2240000 is normal, 1920000-2240000 is performance. > Assume current cpufreq range is powersave, then user want to set it to performance because user wants to play a 3D game. > BUT user have to set it to normal first, then set it to performance because min(performance) > max(powersave)..... > I don't know how people(end-user) would think about such behavior.... why we must be back to normal first, then performance? > > As for the patch I mentioned above which could magically fix them. > The solution is: change store_scaling_max_freq and store_scaling_min_freq sysfs callback, let them have *state*. > Always keep the value from user-space. > > patch like: > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 8772346..00e6965 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -615,6 +615,14 @@ static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf) > static int cpufreq_set_policy(struct cpufreq_policy *policy, > struct cpufreq_policy *new_policy); > > +static void > +cpufreq_get_user_policy_freq(struct cpufreq_real_policy *user_policy, > + struct cpufreq_policy *policy) > +{ > + policy->min = user_policy->min; > + policy->max = user_policy->max; > +} > + > /** > * cpufreq_per_cpu_attr_write() / store_##file_name() - sysfs write access > */ > @@ -622,21 +630,20 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, > static ssize_t store_##file_name \ > (struct cpufreq_policy *policy, const char *buf, size_t count) \ > { \ > - int ret, temp; \ > + int ret; \ > struct cpufreq_policy new_policy; \ > \ > ret = cpufreq_get_policy(&new_policy, policy->cpu); \ > if (ret) \ > return -EINVAL; \ > \ > + cpufreq_get_user_policy_freq(&policy->user_policy, &new_policy);\ > ret = sscanf(buf, "%u", &new_policy.object); \ > if (ret != 1) \ > return -EINVAL; \ > \ > - temp = new_policy.object; \ > - ret = cpufreq_set_policy(policy, &new_policy); \ > - if (!ret) \ > - policy->user_policy.object = temp; \ > + policy->user_policy.object = policy->object; \ should be + policy->user_policy.object = new_policy.object; \ sorry for that. > + ret = cpufreq_set_policy(policy, &new_policy); \ > \ > return ret ? ret : count; \ > } > >
> > > Thanks > xinhui > >> Thanks, >> Rafael >>
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