Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757176AbZDCCzV (ORCPT ); Thu, 2 Apr 2009 22:55:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753026AbZDCCzE (ORCPT ); Thu, 2 Apr 2009 22:55:04 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:60643 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752554AbZDCCzD (ORCPT ); Thu, 2 Apr 2009 22:55:03 -0400 Message-ID: <49D57A82.1030006@garzik.org> Date: Thu, 02 Apr 2009 22:54:58 -0400 From: Jeff Garzik User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: "Trenton D. Adams" CC: Linus Torvalds , Andrew Morton , David Rees , Linux Kernel Mailing List Subject: Re: Linux 2.6.29 References: <20090325183011.GN32307@mit.edu> <20090401210337.GB3797@csclub.uwaterloo.ca> <20090402110532.GA5132@aniel> <72dbd3150904020929w46c6dc0bs4028c49dd8fa8c56@mail.gmail.com> <20090402094247.9d7ac19f.akpm@linux-foundation.org> <49D53787.9060503@garzik.org> <49D56DF6.5020300@garzik.org> <9b1675090904021938q6600bb94m2f9fa1b23316162a@mail.gmail.com> In-Reply-To: <9b1675090904021938q6600bb94m2f9fa1b23316162a@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.4 (----) X-Spam-Report: SpamAssassin version 3.2.5 on srv5.dvmed.net summary: Content analysis details: (-4.4 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1199 Lines: 34 Trenton D. Adams wrote: > On Thu, Apr 2, 2009 at 8:01 PM, Jeff Garzik wrote: >> Linus Torvalds wrote: >> The most interesting thing I found: the SSD does 80 MB/s for the first ~1 >> GB or so, then slows down dramatically. After ~2GB, it is down to 32 MB/s. >> After ~4GB, it reaches a steady speed around 23 MB/s. > > Isn't that the kernel IO queue, and the dd averaging of transfer > speed? For example, once you hit the dirty ratio limit, that is when > it starts writing to disk. So, the first bit you'll see really fast > speeds, as it goes to memory, but it averages out over time to a > slower speed. As an example... overwrite.c is a special program that does this, in a loop: write(buffer-N) data to pagecache start buffer-N write-out to storage wait for buffer-(N-1) write-out to complete It uses the sync_file_range() system call, which is like fsync() on steroids, wearing cool sunglasses. Regards, Jeff -- 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/