linux-kernel - Re: [PATCH v2 1/3] Documentation: admin-guide: pm: Add efficiency vs. latency tradeoff to uncore documentation

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Message-ID: <71e6475c99e193c4ae6e5d45b72b528cdf5f3f62.camel@linux.intel.com>
Date: Fri, 30 Aug 2024 10:23:14 +0300
From: Tero Kristo <tero.kristo@...ux.intel.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
 srinivas.pandruvada@...ux.intel.com,  platform-driver-x86@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] Documentation: admin-guide: pm: Add efficiency
 vs. latency tradeoff to uncore documentation

   1. On Thu, 2024-08-29 at 14:39 +0300, Tero Kristo wrote:
> On Thu, 2024-08-29 at 12:18 +0300, Ilpo Järvinen wrote:
> > On Wed, 28 Aug 2024, Tero Kristo wrote:
> > 
> > > Added documentation about the functionality of efficiency vs.
> > > latency tradeoff
> > > control in intel Xeon processors, and how this is configured via
> > > sysfs.
> > > 
> > > Signed-off-by: Tero Kristo <tero.kristo@...ux.intel.com>
> > > ---
> > > v2:
> > >   * Largely re-wrote the documentation
> > > 
> > >  .../pm/intel_uncore_frequency_scaling.rst     | 59
> > > +++++++++++++++++++
> > >  1 file changed, 59 insertions(+)
> > > 
> > > diff --git a/Documentation/admin-
> > > guide/pm/intel_uncore_frequency_scaling.rst
> > > b/Documentation/admin-
> > > guide/pm/intel_uncore_frequency_scaling.rst
> > > index 5ab3440e6cee..26ded32b06f5 100644
> > > --- a/Documentation/admin-
> > > guide/pm/intel_uncore_frequency_scaling.rst
> > > +++ b/Documentation/admin-
> > > guide/pm/intel_uncore_frequency_scaling.rst
> > > @@ -113,3 +113,62 @@ to apply at each uncore* level.
> > >  
> > >  Support for "current_freq_khz" is available only at each fabric
> > > cluster
> > >  level (i.e., in uncore* directory).
> > > +
> > > +Efficiency vs. Latency Tradeoff
> > > +-------------------------------
> > > +
> > > +The Efficiency Latency Control (ELC) feature improves
> > > performance
> > > +per watt. With this feature hardware power management algorithms
> > > +optimize trade-off between latency and power consumption. For
> > > some
> > > +latency sensitive workloads further tuning can be done by SW to
> > > +get desired performance.
> > > +
> > > +The hardware monitors the average CPU utilization across all
> > > cores
> > > +in a power domain at regular intervals and decides an uncore
> > > frequency.
> > > +While this may result in the best performance per watt, workload
> > > may be
> > > +expecting higher performance at the expense of power. Consider
> > > an
> > > +application that intermittently wakes up to perform memory reads
> > > on an
> > > +otherwise idle system. In such cases, if hardware lowers uncore
> > > +frequency, then there may be delay in ramp up of frequency to
> > > meet
> > > +target performance.
> > > +
> > > +The ELC control defines some parameters which can be changed
> > > from
> > > SW.
> > > +If the average CPU utilization is below a user defined threshold
> > > +(elc_low_threshold_percent attribute below), the user defined
> > > uncore
> > > +frequency floor frequency will be used (elc_floor_freq_khz
> > > attribute
> > 
> > Consider the following simplification:
> > 
> > "the user defined uncore frequency floor frequency" ->
> > "the user-defined uncore floor frequency"
> > 
> > I think it tells the same even without that first "frequency".
> > 
> > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > 
> 
> Yeah, it looks kind of silly. I think that's just a typo from my
> side,
> thanks for catching.

Do you want me to send a new version of this patch or do you fix it
locally? Rest of the patches don't seem to need any changes atm.

-Tero