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Message-ID: <20151027033636.GG8036@hr-amur2>
Date: Tue, 27 Oct 2015 11:36:36 +0800
From: Huang Rui <ray.huang@....com>
To: Guenter Roeck <linux@...ck-us.net>
CC: Borislav Petkov <bp@...e.de>,
Peter Zijlstra <peterz@...radead.org>,
"Jean Delvare" <jdelvare@...e.de>,
Andy Lutomirski <luto@...capital.net>,
"Andreas Herrmann" <herrmann.der.user@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
"Len Brown" <lenb@...nel.org>,
John Stultz <john.stultz@...aro.org>,
Frédéric Weisbecker <fweisbec@...il.com>,
"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>,
Andreas Herrmann <herrmann.der.user@...glemail.com>,
"Gopalakrishnan, Aravind" <Aravind.Gopalakrishnan@....com>,
Borislav Petkov <bp@...en8.de>,
"Fengguang Wu" <fengguang.wu@...el.com>,
Aaron Lu <aaron.lu@...el.com>, "Li, Tony" <Tony.Li@....com>
Subject: Re: [PATCH v2 07/10] hwmon: (fam15h_power) Introduce a cpu
accumulated power reporting algorithm
On Fri, Oct 23, 2015 at 10:20:59PM +0800, Guenter Roeck wrote:
> On 10/19/2015 07:28 PM, Huang Rui wrote:
> > This patch introduces an algorithm that computes the average power by
> > reading a delta value of “core power accumulator” register during
> > measurement interval, and then dividing delta value by the length of
> > the time interval.
> >
> > User is able to use power1_average entry to measure the processor power
> > consumption and power1_average_interval entry to set the interval.
> >
> > A simple example:
> >
> > ray@...ub:~/tip$ sensors
> > fam15h_power-pci-00c4
> > Adapter: PCI adapter
> > power1: 23.73 mW (avg = 634.63 mW, interval = 0.01 s)
> > (crit = 15.00 W)
> >
> > ...
> >
> > The result is current average processor power consumption in 10
> > millisecond. The unit of the result is uWatt.
> >
> > Suggested-by: Guenter Roeck <linux@...ck-us.net>
> > Signed-off-by: Huang Rui <ray.huang@....com>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > ---
> > drivers/hwmon/fam15h_power.c | 120 +++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 120 insertions(+)
> >
> > diff --git a/drivers/hwmon/fam15h_power.c b/drivers/hwmon/fam15h_power.c
> > index 6321f73..a5a539e 100644
> > --- a/drivers/hwmon/fam15h_power.c
> > +++ b/drivers/hwmon/fam15h_power.c
> > @@ -26,6 +26,9 @@
> > #include <linux/pci.h>
> > #include <linux/bitops.h>
> > #include <linux/cpumask.h>
> > +#include <linux/mutex.h>
> > +#include <linux/time.h>
> > +#include <linux/sched.h>
> > #include <asm/processor.h>
> > #include <asm/msr.h>
> >
> > @@ -64,6 +67,10 @@ struct fam15h_power_data {
> > u64 cu_acc_power[MAX_CUS];
> > /* performance timestamp counter */
> > u64 cpu_sw_pwr_ptsc[MAX_CUS];
> > + /* online/offline status of current compute unit */
> > + int cu_on[MAX_CUS];
> > + unsigned long power_period;
> > + struct mutex acc_pwr_mutex;
>
> Can you elaborate a bit about what this mutex is supposed to protect ?
> To me it seems that it doesn't really protect anything.
>
My orignal intention is to avoid race condition from user space.
Actually you know, show_power_acc, acc_set_power_period will expose to
application layer.
> > };
> >
> > static ssize_t show_power(struct device *dev,
> > @@ -132,11 +139,15 @@ static void do_read_registers_on_cu(void *_data)
> > cores_per_cu = amd_get_cores_per_cu();
> > cu = cpu / cores_per_cu;
> >
> > + mutex_lock(&data->acc_pwr_mutex);
> > WARN_ON(rdmsrl_safe(MSR_F15H_CU_PWR_ACCUMULATOR,
> > &data->cu_acc_power[cu]));
> >
> > WARN_ON(rdmsrl_safe(MSR_F15H_PTSC,
> > &data->cpu_sw_pwr_ptsc[cu]));
> > +
> > + data->cu_on[cu] = 1;
> > + mutex_unlock(&data->acc_pwr_mutex);
>
> ... for example, while this protects cu_on[cu],
>
> > }
> >
> > static int read_registers(struct fam15h_power_data *data)
> > @@ -148,6 +159,10 @@ static int read_registers(struct fam15h_power_data *data)
> > cores_per_cu = amd_get_cores_per_cu();
> > cu_num = boot_cpu_data.x86_max_cores / cores_per_cu;
> >
> > + mutex_lock(&data->acc_pwr_mutex);
> > + memset(data->cu_on, 0, sizeof(int) * MAX_CUS);
> > + mutex_unlock(&data->acc_pwr_mutex);
>
> ... this code may well overwrite that same value.
>
Yes, but I only need the compute unit status of the "sencond" time of read_registers.
Then ignore the offline compute unit to avoid hotplug issue.
> > +
> > WARN_ON_ONCE(cu_num > MAX_CUS);
> >
> > ret = zalloc_cpumask_var(&mask, GFP_KERNEL);
> > @@ -184,18 +199,113 @@ static int read_registers(struct fam15h_power_data *data)
> > return 0;
> > }
> >
> > +static ssize_t acc_show_power(struct device *dev,
> > + struct device_attribute *attr,
> > + char *buf)
> > +{
> > + struct fam15h_power_data *data = dev_get_drvdata(dev);
> > + u64 prev_cu_acc_power[MAX_CUS], prev_ptsc[MAX_CUS],
> > + jdelta[MAX_CUS];
> > + u64 tdelta, avg_acc;
> > + int cu, cu_num, cores_per_cu, ret;
> > + signed long leftover;
> > +
> > + cores_per_cu = amd_get_cores_per_cu();
> > + cu_num = boot_cpu_data.x86_max_cores / cores_per_cu;
> > +
> > + ret = read_registers(data);
> > + if (ret)
> > + return 0;
The first time of read_registers
> > +
> > + cu = 0;
> > + while(cu++ < cu_num) {
> > + prev_cu_acc_power[cu] = data->cu_acc_power[cu];
> > + prev_ptsc[cu] = data->cpu_sw_pwr_ptsc[cu];
> > + }
>
> ... and multiple parallel reads on the power attribute must produce
> pretty random values, unless I am really missing something.
>
> > +
> > + leftover = schedule_timeout_interruptible(
> > + msecs_to_jiffies(data->power_period)
> > + );
> > + if (leftover)
> > + return 0;
> > +
> > + ret = read_registers(data);
The second time of read_registers
> > + if (ret)
> > + return 0;
> > +
> With a 10ms period, I wonder how accurate this really is.
>
According to the HW description, the measurement interval could be on
the order of several milliseconds. That should get a stable average
power value.
> > + for (cu = 0, avg_acc = 0; cu < cu_num; cu++) {
> > + /* check if current compute unit is online */
> > + if (data->cu_on[cu] == 0)
> > + continue;
> > +
> > + if (data->cu_acc_power[cu] < prev_cu_acc_power[cu]) {
> > + jdelta[cu] = data->max_cu_acc_power + data->cu_acc_power[cu];
> > + jdelta[cu] -= prev_cu_acc_power[cu];
> > + } else {
> > + jdelta[cu] = data->cu_acc_power[cu] - prev_cu_acc_power[cu];
> > + }
> > + tdelta = data->cpu_sw_pwr_ptsc[cu] - prev_ptsc[cu];
> > + jdelta[cu] *= data->cpu_pwr_sample_ratio * 1000;
> > + do_div(jdelta[cu], tdelta);
> > +
> > + /* the unit is microWatt */
> > + avg_acc += jdelta[cu];
> > + }
> > +
> > + return sprintf(buf, "%llu\n", (unsigned long long)avg_acc);
> > +}
> > +static DEVICE_ATTR(power1_average, S_IRUGO, acc_show_power, NULL);
> > +
> > +
> > +static ssize_t acc_show_power_period(struct device *dev,
> > + struct device_attribute *attr,
> > + char *buf)
> > +{
> > + struct fam15h_power_data *data = dev_get_drvdata(dev);
> > +
> > + return sprintf(buf, "%lu\n", data->power_period);
> > +}
> > +
> > +static ssize_t acc_set_power_period(struct device *dev,
> > + struct device_attribute *attr,
> > + const char *buf, size_t count)
> > +{
> > + struct fam15h_power_data *data = dev_get_drvdata(dev);
> > + unsigned long temp;
> > + int ret;
> > +
> > + ret = kstrtoul(buf, 10, &temp);
> > + if (ret)
> > + return ret;
> > +
> > + mutex_lock(&data->acc_pwr_mutex);
> > + data->power_period = temp;
> > + mutex_unlock(&data->acc_pwr_mutex);
>
> This doesn't really protect anything either except that power_period
> can not be updated while the lock is active. But the code using
> power_period does not run under mutex protection, so that seems pretty
> pointless.
>
I thought about carefully, the mutex here didn't protect the variable.
Actually, my variables such as data->cu_acc_power[cu],
data->cu_on[cu] are independent for different cpu cores. They cannot
be updated on different threads at the same time. Different threads
just only updates values on different cu(index).
> Also, this accepts an unlimited timeout. If I understand correctly,
> setting the timeout to, say, 10 seconds will cause the read function
> to hang for that period of time. Setting it to 1 hour will cause the read
> function to hang for 1 hour.
>
> Does this really make sense ?
>
You're right. If set a long interval, the mutex will be hold a long
time, that causes cpu looks stuck...
So should I set a "power1_average_max"?
Thanks,
Rui
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