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....@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; \ + ret = cpufreq_set_policy(policy, &new_policy); \ \ return ret ? ret : count; \ } Thanks xinhui > Thanks, > Rafael > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/