From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Zhang, Yanmin" Subject: Dynamic configure max_cstate Date: Mon, 27 Jul 2009 13:30:13 +0800 Message-ID: <1248672613.2560.604.camel@ymzhang> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from mga07.intel.com ([143.182.124.22]:23979 "EHLO azsmga101.ch.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752613AbZG0FaE (ORCPT ); Mon, 27 Jul 2009 01:30:04 -0400 Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: LKML , linux-acpi@vger.kernel.org Cc: yakui_zhao When running a fio workload, I found sometimes cpu C state has big impact on the result. Mostly, fio is a disk I/O workload which doesn't spend much time with cpu, so cpu switch to C2/C3 freqently and the latency is big. If I start kernel with idle=poll or processor.max_cstate=1, the result is quite good. Consider a scenario that machine is busy at daytime and free at night. Could we add a dynamic configuration interface for processor.max_cstate or something similiar with sysfs? So user applications could change the max_cstate dynamically? For example, we could add a new parameter to function cpuidle_governor->select to mark the highest c state. Any idea? Yanmin