From patchwork Sun Jun 2 01:24:12 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Finn Thain X-Patchwork-Id: 10971591 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B507B1575 for ; Sun, 2 Jun 2019 01:29:36 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A54F428B92 for ; Sun, 2 Jun 2019 01:29:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 99A2F28BB0; Sun, 2 Jun 2019 01:29:36 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4380928B92 for ; Sun, 2 Jun 2019 01:29:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726823AbfFBB3K (ORCPT ); Sat, 1 Jun 2019 21:29:10 -0400 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:34636 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726485AbfFBB3J (ORCPT ); Sat, 1 Jun 2019 21:29:09 -0400 Received: by kvm5.telegraphics.com.au (Postfix, from userid 502) id 0698F27EC3; Sat, 1 Jun 2019 21:29:06 -0400 (EDT) To: "James E.J. Bottomley" , "Martin K. Petersen" Cc: "Michael Schmitz" , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Message-Id: <666248afffd5a75c3259f06737ddcfb2b833b1f7.1559438652.git.fthain@telegraphics.com.au> In-Reply-To: References: From: Finn Thain Subject: [PATCH 4/7] scsi: mac_scsi: Increase PIO/PDMA transfer length threshold Date: Sun, 02 Jun 2019 11:24:12 +1000 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Some targets introduce delays when handshaking the response to certain commands. For example, a disk may send a 96-byte response to an INQUIRY command (or a 24-byte response to a MODE SENSE command) too slowly. Apparently the first 12 or 14 bytes are handshaked okay but then the system bus error timeout is reached while transferring the next word. Since the scsi bus phase hasn't changed, the driver then sets the target borken flag to prevent further PDMA transfers. The driver also logs the warning, "switching to slow handshake". Raise the PDMA threshold to 512 bytes so that PIO transfers will be used for these commands. This default is sufficiently low that PDMA will still be used for READ and WRITE commands. The existing threshold (16 bytes) was chosen more or less at random. However, best performance requires the threshold to be as low as possible. Those systems that don't need the PIO workaround at all may benefit from mac_scsi.setup_use_pdma=1 Cc: Michael Schmitz Cc: stable@vger.kernel.org # v4.14+ Fixes: 3a0f64bfa907 ("mac_scsi: Fix pseudo DMA implementation") Tested-by: Stan Johnson Signed-off-by: Finn Thain --- drivers/scsi/mac_scsi.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/scsi/mac_scsi.c b/drivers/scsi/mac_scsi.c index 8b4b5b1a13d7..ba1afcaadae8 100644 --- a/drivers/scsi/mac_scsi.c +++ b/drivers/scsi/mac_scsi.c @@ -52,7 +52,7 @@ static int setup_cmd_per_lun = -1; module_param(setup_cmd_per_lun, int, 0); static int setup_sg_tablesize = -1; module_param(setup_sg_tablesize, int, 0); -static int setup_use_pdma = -1; +static int setup_use_pdma = 512; module_param(setup_use_pdma, int, 0); static int setup_hostid = -1; module_param(setup_hostid, int, 0); @@ -305,7 +305,7 @@ static int macscsi_dma_xfer_len(struct NCR5380_hostdata *hostdata, struct scsi_cmnd *cmd) { if (hostdata->flags & FLAG_NO_PSEUDO_DMA || - cmd->SCp.this_residual < 16) + cmd->SCp.this_residual < setup_use_pdma) return 0; return cmd->SCp.this_residual;