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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 21A64C2BA19 for ; Sun, 19 Apr 2020 00:35:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E29072076A for ; Sun, 19 Apr 2020 00:35:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=lunn.ch header.i=@lunn.ch header.b="4ZgjXG6Z" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725879AbgDSAfI (ORCPT ); Sat, 18 Apr 2020 20:35:08 -0400 Received: from vps0.lunn.ch ([185.16.172.187]:47324 "EHLO vps0.lunn.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725804AbgDSAfI (ORCPT ); Sat, 18 Apr 2020 20:35:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lunn.ch; s=20171124; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=zJk5ZNxWAF8NZypDghNXSxmU6TnWhH8GjElwssejEoc=; b=4ZgjXG6ZwVpfc7K+fZLNj/QobN JdczcXhbNeaPvj2mChFqeYrKf2ufH2V5PghWZiuxOw9mrgEJaXBzcEpdCr8qaKGLV4CO2XAG9oIuS IppBe37h23aw71NModehYqmPHAB4LSNrAy6Ym/Q3vfVhOk1oagCDKtPEktbQxpQPfNms=; Received: from andrew by vps0.lunn.ch with local (Exim 4.93) (envelope-from ) id 1jPxvJ-003Xud-8N; Sun, 19 Apr 2020 02:35:01 +0200 Date: Sun, 19 Apr 2020 02:35:01 +0200 From: Andrew Lunn To: Chris Healy Cc: Andy Duan , David Miller , netdev , Florian Fainelli , Heiner Kallweit Subject: Re: [EXT] [PATCH net-next v2 1/3] net: ethernet: fec: Replace interrupt driven MDIO with polled IO Message-ID: <20200419003501.GE836632@lunn.ch> References: <20200418000355.804617-1-andrew@lunn.ch> <20200418000355.804617-2-andrew@lunn.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, Apr 18, 2020 at 03:39:17PM -0700, Chris Healy wrote: > I did some profiling using an oscilloscope with my NXP Vybrid based > platform to see what different "sleep_us" values resulted in for start > of MDIO to start of MDIO transaction times. Here's what I found: > > 0 - ~38us to ~40us > 1 - ~48us to ~64us > 2 - ~48us to ~64us > 3 - ~48us to ~64us > 4 - ~48us to ~64us > 4 - ~48us to ~64us > 5 - ~48us to ~64us > 6 - ~48us to ~64us > 7 - ~48us to ~64us > 8 - ~48us to ~64us > 9 - ~56us to ~88us > 10 - ~56us to ~112us > > Basically, with the "sleep_us" value set to 0, I would get the > shortest inter transaction times with a very low variance. Once I > went to a non-zero value, the inter transaction time went up, as well > as the variance, which I suppose makes sense.... Thanks for these numbers. They are suggesting that udelay() is quite expensive, and is probably taking longer than we expect. I might instrument the function to see what is happening. Andrew