On Fri, Mar 22, 2019 at 3:46 PM Borislav Petkov <b...@alien8.de> wrote: > > First of all, thanks a lot for doing that! > > This is a good example for how we should convert all the /dev/msr > accessing tools. > > Nitpicks below. > > On Thu, Mar 21, 2019 at 11:20:17PM +0100, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > > > The Performance and Energy Bias Hint (EPB) is expected to be set by > > user space through the generic MSR interface, but that interface is > > not particularly nice and there are security concerns regarding it, > > so it is not always available. > > > > For this reason, add a sysfs interface for reading and updating the > > EPB, in the form of a new attribute, energy_perf_bias, located > > under /sys/devices/system/cpu/cpu#/power/ for online CPUs that > > support the EPB feature. > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > --- > > Documentation/ABI/testing/sysfs-devices-system-cpu | 18 ++++ > > Documentation/admin-guide/pm/intel_epb.rst | 27 ++++++ > > arch/x86/kernel/cpu/intel_epb.c | 93 > > ++++++++++++++++++++- > > 3 files changed, 134 insertions(+), 4 deletions(-) > > ... > > > +static ssize_t energy_perf_bias_show(struct device *dev, > > + struct device_attribute *attr, > > + char *buf) > > +{ > > + unsigned int cpu = dev->id; > > + u64 epb; > > + int ret; > > + > > + ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb); > > That's an IPI and an MSR read each time. You could dump saved_epb > instead, no?
No, because the MSR can change in ways beyond control of this code sometimes. Generally, saved_epb only is the right value at the CPU online time. > > + if (ret < 0) > > + return ret; > > + > > + return sprintf(buf, "%llu\n", epb); > > +} > > + > > +static ssize_t energy_perf_bias_store(struct device *dev, > > + struct device_attribute *attr, > > + const char *buf, size_t count) > > +{ > > + unsigned int cpu = dev->id; > > + u64 epb, val; > > + int ret; > > + > > + ret = __sysfs_match_string(energy_perf_strings, > > + ARRAY_SIZE(energy_perf_strings), buf); > > + if (ret >= 0) > > + val = energ_perf_values[ret]; > > + else if (kstrtou64(buf, 0, &val) || val > MAX_EPB) > > Range is 0 - 15 but u64? Maybe make it an u8? :) At the cost of an extra conversion below, right? > > + return -EINVAL; > > + > > + ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb); > > + if (ret < 0) > > + return ret; > > + > > + ret = wrmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, > > + (epb & ~EPB_MASK) | val); > > + if (ret < 0) > > + return ret; > > + > > + return count; > > +} > > --