From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753890AbbBJT0K (ORCPT ); Tue, 10 Feb 2015 14:26:10 -0500 Received: from mx1.HRZ.tu-dortmund.de ([129.217.128.51]:40661 "EHLO unimail.uni-dortmund.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753342AbbBJT0I (ORCPT ); Tue, 10 Feb 2015 14:26:08 -0500 X-Greylist: delayed 2052 seconds by postgrey-1.27 at vger.kernel.org; Tue, 10 Feb 2015 14:26:08 EST Date: Tue, 10 Feb 2015 19:50:36 +0100 From: Andrej Gelenberg To: JBottomley@parallels.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, hch@lst.de, martin.petersen@oracle.com, elliott@hp.com Subject: CONFIG_SCSI_MQ_DEFAULT cause slow direct write speed to usb stick Message-ID: <20150210195036.3dce0e9e@bigpc> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, i had found a problem with CONFIG_SCSI_MQ_DEFAULT config option. If it activated, then the write speeds to the /dev/sd* of an usb stick drops dramatically: it's only about 250 kb/CONFIG_SCSI_MQ_DEFAULTs, but should be about 7 Mb/s. Git bisect also points to commit 24c20f10583647e30afe87b6f6d5e14bc7b1cbc6 'scsi: add a CONFIG_SCSI_MQ_DEFAULT option' (i always set CONFIG_SCSI_MQ_DEFAULT to y, because it sounded interesting). Same problem is also in 3.19 present. Write speeds to a filesystem on that USB-Stick were not so bad, but as i tried to dd in Live-DVD Ubuntu image it was painfully slow. After i disabled CONFIG_SCSI_MQ_DEFAULT write speeds are back to normal. I created bug report in bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=92571 Regards, Andrej