From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753758AbaIPIz0 (ORCPT ); Tue, 16 Sep 2014 04:55:26 -0400 Received: from michael.mail.tiscali.it ([213.205.33.246]:41728 "EHLO michael.mail.tiscali.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753173AbaIPIzM (ORCPT ); Tue, 16 Sep 2014 04:55:12 -0400 Message-ID: <5417FB30.8030908@assyoma.it> Date: Tue, 16 Sep 2014 10:56:16 +0200 From: Gionatan Danti Organization: Assyoma s.r.l. User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org CC: g.danti@assyoma.it Subject: Re: AHCI maximum transfer size References: In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Hi all, > I searched the list and the internet for this question, but I did not > find a definitive answer. > > I wonder what is the maximum AHCI transfer size for kernel 2.6.32.x > Let me explain: using a command as "dd if=/dev/zero of=/dev/sda bs=2M" I > can see, via iostat, that request-size is at 2M (as expected). However > it seems to me that the effective transfer size is way lower: disabling > writeback cache on the target disk, I see very low performance even for > big-chunk transfers. > > Googling, I found this post on stackoverflow stating that maximum > observerd AHCI transfer size (with a SATA protocol analyzer) is 128KB: > http://stackoverflow.com/questions/24053662/how-to-enlarge-sata-transfer-size-in-linux-ahci-driver. > > The stackoverflow post seems to agree with this old LWN.net article: > http://lwn.net/Articles/77981/ > > Anyone has any idea of how to find (and eventually change) the used AHCI > transfer size without touching the code? > > NOTE: please CC me directly. > Regards. > Hi all, any idea on the subject? Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8