From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Lord Subject: Re: Why so much PIO for r/w accesses ? Date: Sun, 21 Nov 2010 18:39:51 -0500 Message-ID: <4CE9ADC7.8040800@teksavvy.com> References: <4CE9ACAA.9060203@teksavvy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from ironport2-out.teksavvy.com ([206.248.154.181]:4456 "EHLO ironport2-out.pppoe.ca" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754768Ab0KUXjx (ORCPT ); Sun, 21 Nov 2010 18:39:53 -0500 In-Reply-To: <4CE9ACAA.9060203@teksavvy.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: IDE/ATA development list , Jeff Garzik , Tejun Heo On 10-11-21 06:35 PM, Mark Lord wrote: > While working on something unrelated today, > I instrumented ata_sff_data_xfer32() to generate a printk() on each invocation. > > Imagine then my complete surprise to see that print() being invoked very frequently > after rebooting with the modified kernel. > > ata_sff_data_xfer32() is for PIO read/writes.. something that I don't expect to > see. > > This is an ata_piix system, with a pure SATA SSD. > Why are we using PIO so much? > Or am I simply misunderstanding something basic here.. ? > > Confused. Definitely just me being confused. :) I changed the printk() into an ata_dev_printk(), and discovered that all of those reads/writes are targeting the DVD-RW drive, not the SSD. So this is simply hald or something similar polling for disc-insertion, and PIO is used (as always) for the PACKET command transfer. Duh. :)