Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261722AbVAEGxX (ORCPT ); Wed, 5 Jan 2005 01:53:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262267AbVAEGxW (ORCPT ); Wed, 5 Jan 2005 01:53:22 -0500 Received: from pri-dns2.mtco.com ([207.179.200.252]:26587 "HELO pri-dns2.mtco.com") by vger.kernel.org with SMTP id S261722AbVAEGxN (ORCPT ); Wed, 5 Jan 2005 01:53:13 -0500 From: Tom Felker To: "tony osborne" Subject: Re: Main CPU- I/O CPU interaction Date: Wed, 5 Jan 2005 00:53:13 -0600 User-Agent: KMail/1.7.2 Cc: linux-kernel@vger.kernel.org References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200501050053.13744.tfelker2@uiuc.edu> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1700 Lines: 43 On Sunday 02 January 2005 06:44 pm, tony osborne wrote: > Hello, > > I wish to be personally CC'ed the answers/comments posted to the list in > response to this post . > > > The I/O devices are equipped with dedicated processor to free the main CPU > from doing the low level I/O operations. However, if i am editing and > updating a big size file and i want to save > it afterwards, i notice my PC getting blocked while saving the file which > theoritically should NOT happen as it is up to the I/O device processor and > not the main CPU to save the data into the disk; the main CPU could switch > to another process after giving the high level command -save-to the device > processor; so why the main CPU is blocked while saving such big size files > > thanks Check to make sure DMA is on: hdparm /dev/hda If not, try turning it on: hdparm -d 1 /dev/hda When it's not on, you'll get bad performance (I usually get around 2 MB/s according to "hdparm -t /dev/hda") and high system CPU usage. Because the rate is so low, for big files, the high CPU usage starves other processes for long enough that you notice. With DMA, the transfer will be much faster and the CPU usage will be minimal. -- Tom Felker, - Stop fiddling with the volume knob. If nature has made any one thing less susceptible than all others of exclusive property, it is the action of the thinking power called an idea. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/