From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>, x86 <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Len Brown <len.brown@intel.com>,
Linux PM <linux-pm@vger.kernel.org>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Laura Abbott <labbott@fedoraproject.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Simon Schricker <sschricker@suse.de>,
Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS sysfs interface
Date: Mon, 25 Mar 2019 11:01:08 +0100 [thread overview]
Message-ID: <CAJZ5v0iML0dvzLszSnZjBPKc=2fWp4aUxEjAYWjJnz41Kz8w1g@mail.gmail.com> (raw)
In-Reply-To: <20190322144629.GC12472@zn.tnic>
On Fri, Mar 22, 2019 at 3:46 PM Borislav Petkov <bp@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.wysocki@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.wysocki@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;
> > +}
>
> --
next prev parent reply other threads:[~2019-03-25 10:01 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-21 22:12 [PATCH 0/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS handling fixes and sysfs i/f Rafael J. Wysocki
2019-03-21 22:18 ` [PATCH 1/2] PM / arch: x86: Rework the MSR_IA32_ENERGY_PERF_BIAS handling Rafael J. Wysocki
2019-03-22 9:03 ` Hannes Reinecke
2019-03-22 14:28 ` Borislav Petkov
2019-03-22 14:31 ` Thomas Gleixner
2019-03-22 14:35 ` Borislav Petkov
2019-03-22 16:12 ` Thomas Gleixner
2019-03-22 16:52 ` Joe Perches
2019-03-25 10:06 ` Rafael J. Wysocki
2019-03-22 16:27 ` Thomas Renninger
2019-03-22 16:43 ` Borislav Petkov
2019-03-25 11:31 ` Borislav Petkov
2019-03-21 22:20 ` [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS sysfs interface Rafael J. Wysocki
2019-03-22 9:03 ` Hannes Reinecke
2019-03-22 14:46 ` Borislav Petkov
2019-03-25 10:01 ` Rafael J. Wysocki [this message]
2019-03-22 15:00 ` Peter Zijlstra
2019-03-25 9:56 ` Rafael J. Wysocki
2019-03-25 11:32 ` Borislav Petkov
2019-05-09 10:23 ` Ido Schimmel
2019-05-09 17:18 ` Rafael J. Wysocki
2019-05-09 17:43 ` Ido Schimmel
2019-05-09 21:28 ` [PATCH] x86: intel_epb: Take CONFIG_PM into account Rafael J. Wysocki
2019-05-10 6:01 ` Ingo Molnar
2019-05-27 10:56 ` [PATCH] x86: intel_epb: Do not build when CONFIG_PM is unset Rafael J. Wysocki
2019-05-30 7:47 ` Ingo Molnar
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