From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pan Xinhui Subject: Re: [PATCH] cpufreq: Add scaling frequency range support Date: Wed, 29 Jul 2015 18:04:56 +0800 Message-ID: <55B8A548.4060104@intel.com> References: <55B6F7C3.8040405@intel.com> <20150728042945.GE1229@linux> <55B70ACD.9010402@intel.com> <15808229.KgKF05ecju@vostro.rjw.lan> <55B8A3F2.8030809@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mga03.intel.com ([134.134.136.65]:54590 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751101AbbG2KHZ (ORCPT ); Wed, 29 Jul 2015 06:07:25 -0400 In-Reply-To: <55B8A3F2.8030809@intel.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: Viresh Kumar , "linux-kernel@vger.kernel.org" , "linux-pm@vger.kernel.org" , "mnipxh@163.com" , "yanmin_zhang@linux.intel.com" On 2015=E5=B9=B407=E6=9C=8829=E6=97=A5 17:59, Pan Xinhui wrote: > hi, Rafael > thanks for you reply. >=20 > On 2015=E5=B9=B407=E6=9C=8829=E6=97=A5 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=E5=B9=B407=E6=9C=8828=E6=97=A5 12:29, Viresh Kumar wrote: >>>> On 28-07-15, 11:32, Pan Xinhui wrote: >>>>> From: Pan Xinhui >>>>> >>>>> 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_f= req >>>>> echo 2240000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_f= req >>>>> >>>>> Add scaling_freq_range cpufreq attr to support userspace's demand= =2E >>>>> Therefore it's easier for testers to write readable scripts like = below:=20 >>>>> 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_fre= q >>> echo 960000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq >>> .....//other works >>> echo 1120000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_fr= eq >>> echo 2240000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_fre= q >>> ...//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 scr= ipts. >> >> Fix them, then, pretty please. >> > of course we will fix them. :) >=20 >> 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 h= ave another patch which could magically fix them. :) >=20 > 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 examp= le, proc/sys/fs/file-max. > As the file-min is always zero. It's very reasonable to only support = file-max attribute file. >=20 > The sequence we echoing value to min/max_freq is very important. Mayb= e we can also assume they have *state*. > Just like a developer writes a buf to a file. he should do in this wa= y below. > fp =3D fopen(..) > =3D> fwrite(...) > =3D> fclose(...) >=20 > 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. >=20 > 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 off= er 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) >=20 > What if we offer *set freq range* attribute? just once. :) > set freq range (system call one time) >=20 > From performance point, It's a good idea to offer such attribute. >=20 > There is another reason for why it's good to apply this patch. > If cpufreg range is 480000-960000, we call it powersave, 480000-22400= 00 is normal, 1920000-2240000 is performance. > Assume current cpufreq range is powersave, then user want to set it t= o performance because user wants to play a 3D game. > BUT user have to set it to normal first, then set it to performance b= ecause 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? >=20 > 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. >=20 > 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 cpuf= req_policy *policy, char *buf) > static int cpufreq_set_policy(struct cpufreq_policy *policy, > struct cpufreq_policy *new_policy); > =20 > +static void > +cpufreq_get_user_policy_freq(struct cpufreq_real_policy *user_policy= , > + struct cpufreq_policy *policy) > +{ > + policy->min =3D user_policy->min; > + policy->max =3D 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_po= licy *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 =3D cpufreq_get_policy(&new_policy, policy->cpu); = \ > if (ret) = \ > return -EINVAL; = \ > = \ > + cpufreq_get_user_policy_freq(&policy->user_policy, &new_polic= y);\ > ret =3D sscanf(buf, "%u", &new_policy.object); = \ > if (ret !=3D 1) = \ > return -EINVAL; = \ > = \ > - temp =3D new_policy.object; = \ > - ret =3D cpufreq_set_policy(policy, &new_policy); \ > - if (!ret) = \ > - policy->user_policy.object =3D temp; = \ > + policy->user_policy.object =3D policy->object; = \ should be=20 + policy->user_policy.object =3D new_policy.object; \ sorry for that. > + ret =3D cpufreq_set_policy(policy, &new_policy); = \ > = \ > return ret ? ret : count; = \ > } >=20 > >=20 >=20 > Thanks > xinhui >=20 >> Thanks, >> Rafael >>