From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C3EEC43603 for ; Wed, 4 Dec 2019 17:01:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D54B7205ED for ; Wed, 4 Dec 2019 17:01:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729006AbfLDRBf convert rfc822-to-8bit (ORCPT ); Wed, 4 Dec 2019 12:01:35 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:38428 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726934AbfLDRBf (ORCPT ); Wed, 4 Dec 2019 12:01:35 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-99-sjLWNHPnP_GIhzqPZuPVuA-1; Wed, 04 Dec 2019 17:01:32 +0000 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 4 Dec 2019 17:01:32 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Wed, 4 Dec 2019 17:01:32 +0000 From: David Laight To: "x86@kernel.org" , "linux-kernel@vger.kernel.org" Subject: Running an Ivy Bridge cpu at fixed frequency Thread-Topic: Running an Ivy Bridge cpu at fixed frequency Thread-Index: AdWqwtS5CEX1+9oiRRqqz+2UyKDrUw== Date: Wed, 4 Dec 2019 17:01:32 +0000 Message-ID: <8eeee0695c664305ba6a56bce42a995f@AcuMS.aculab.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: sjLWNHPnP_GIhzqPZuPVuA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Is there any way to persuade the intel_pstate driver to make an Ivy bridge (i7-3770) cpu run at a fixed frequency? It is really difficult to compare code execution times when the cpu clock speed keeps changing. I thought I'd managed by setting the 'scaling_max_freq' to 1.7GHz, but even that doesn't seem to be working now. It would also be nice to run a little faster than that - but without it 'randomly' going to 'turbo' frequencies (which it is doing even after I've set no_turbo to 1). An alternative would be a variable frequency TSC - might give more consistent values. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)