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=-3.8 required=3.0 tests=BAYES_00, 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 B23CCC4363D for ; Fri, 2 Oct 2020 19:46:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61312206DD for ; Fri, 2 Oct 2020 19:46:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388466AbgJBTqJ (ORCPT ); Fri, 2 Oct 2020 15:46:09 -0400 Received: from mga11.intel.com ([192.55.52.93]:7799 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387768AbgJBTqI (ORCPT ); Fri, 2 Oct 2020 15:46:08 -0400 IronPort-SDR: V+3nBrR/3obB6h4JCpe4mqzTu9iGGD8f0mtjSAELoXM0S3PsgbS5xkCLpqW0P8EJ/5sd8+gvGi 2TiUrFsYi1JA== X-IronPort-AV: E=McAfee;i="6000,8403,9762"; a="160385404" X-IronPort-AV: E=Sophos;i="5.77,328,1596524400"; d="scan'208";a="160385404" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Oct 2020 12:46:06 -0700 IronPort-SDR: AbMRmWB5KjFD0LhfyDUyVkjeXMVhzrfDHZiXS8OQYkMHX+xZ2Cy/bO4gq3okhbhWvCtH4X9fQG Y0BBfG5axUkQ== X-IronPort-AV: E=Sophos;i="5.77,328,1596524400"; d="scan'208";a="458727838" Received: from ssing11-mobl.amr.corp.intel.com (HELO ellie) ([10.209.68.166]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Oct 2020 12:46:05 -0700 From: Vinicius Costa Gomes To: Eric Dumazet , =?utf-8?B?5Y+25bCP6b6Z?= , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: Why ping latency is smaller with shorter send interval? In-Reply-To: <0d8f732d-03e1-75f0-09fd-520911088c0d@gmail.com> References: <0d8f732d-03e1-75f0-09fd-520911088c0d@gmail.com> Date: Fri, 02 Oct 2020 12:46:04 -0700 Message-ID: <87zh544dj7.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Eric Dumazet writes: > > Many factors in play here. > > 1) if you keep cpus busy enough, they tend to keep in their caches > the data needed to serve your requests. In your case, time taken to > process an ICMP packet can be very different depending on how hot > cpu caches are. > > 2) Idle cpus can be put in a power conserving state. > It takes time to exit from these states, as you noticed. > These delays can typically be around 50 usec, or more. Still on the power management theme, in my experience, in addition to the CPU power states, the PCIe and NIC power management settings also effect latency on the order of 10-100s usecs when the system is allowed to go idle, some things that have helped: - setting CONFIG_PCIEASPM to performance; - disabling EEE (energy efficient ethernet) in your NIC; > > Search for cpu C-states , and powertop program. > Cheers, -- Vinicius