linux-kernel - [PATCH] Documentation: intel_pstate: Describe hwp_dynamic

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Message-ID: <306013127.TOMvMKusHN@aspire.rjw.lan>
Date:   Tue, 26 Jun 2018 17:20:43 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux PM <linux-pm@...r.kernel.org>
Cc:     Linux Documentation <linux-doc@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] Documentation: intel_pstate: Describe hwp_dynamic_boost sysfs knob

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Document the recently introduced hwp_dynamic_boost sysfs knob
allowing user space to tell intel_pstate to use iowait boosting
in the active mode with HWP enabled (to improve performance).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 Documentation/admin-guide/pm/intel_pstate.rst |   11 +++++++++++
 1 file changed, 11 insertions(+)

Index: linux-pm/Documentation/admin-guide/pm/intel_pstate.rst
===================================================================
--- linux-pm.orig/Documentation/admin-guide/pm/intel_pstate.rst
+++ linux-pm/Documentation/admin-guide/pm/intel_pstate.rst
@@ -378,6 +378,17 @@ argument is passed to the kernel in the
 	but it affects the maximum possible value of per-policy P-state	limits
 	(see `Interpretation of Policy Attributes`_ below for details).
 
+``hwp_dynamic_boost``
+	This attribute is only present if ``intel_pstate`` works in the
+	`active mode with the HWP feature enabled <Active Mode With HWP_>`_ in
+	the processor.  If set (equal to 1), it causes the minimum P-state limit
+	to be increased dynamically for a short time whenever a task previously
+	waiting on I/O is selected to run on a given logical CPU (the purpose
+	of this mechanism is to improve performance).
+
+	This setting has no effect on logical CPUs whose minimum P-state limit
+	is directly set to the highest non-turbo P-state or above it.
+
 .. _status_attr:
 
 ``status``