From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751248AbdJDWq1 (ORCPT ); Wed, 4 Oct 2017 18:46:27 -0400 Received: from mga11.intel.com ([192.55.52.93]:31698 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751177AbdJDWq0 (ORCPT ); Wed, 4 Oct 2017 18:46:26 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.42,478,1500966000"; d="scan'208";a="156829015" From: Srinivas Pandruvada To: corbet@lwn.net, rjw@rjwysocki.net Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Srinivas Pandruvada Subject: [PATCH] cpufreq: intel_pstate: Clarify effective CPU frequency Date: Wed, 4 Oct 2017 15:46:16 -0700 Message-Id: <1507157176-54361-1-git-send-email-srinivas.pandruvada@linux.intel.com> X-Mailer: git-send-email 2.7.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add section for resultant frequency during GPU workloads. Signed-off-by: Srinivas Pandruvada --- Documentation/admin-guide/pm/intel_pstate.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-guide/pm/intel_pstate.rst index d2b6fda..a7c6308 100644 --- a/Documentation/admin-guide/pm/intel_pstate.rst +++ b/Documentation/admin-guide/pm/intel_pstate.rst @@ -482,6 +482,25 @@ on the following rules, regardless of the current operation mode of the driver: 3. The global and per-policy limits can be set independently. +One important point to note is that all the above limit controls including +``no_turbo``, only limits the P-state requests by the intel_pstate driver. The +actual performance delivered by the processor is also influenced by GPU +(Graphics processing unit) for GPU bound workloads. So, it is possible +that, while GPU is requesting higher frequencies, the resultant P-state +(CPU frequency) can be higher than the limits set via sysfs. +Equivalent limits must, therefore, also be set for the GPU. + +An example where an Intel i915 GPU is used: + +#cat /sys/kernel/debug/dri/0/i915_ring_freq_table + +displays effective CPU frequency for a GPU frequency. To limit +a CPU frequency, a corresponding GPU frequency limit must also be placed: + +/sys/class/drm/card0/gt_max_freq_mhz and + +/sys/class/drm/card0/gt_boost_freq_mhz + If the `HWP feature is enabled in the processor `_, the resulting effective values are written into its registers whenever the limits change in order to request its internal P-state selection logic to always set -- 2.7.5