From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755353AbcH1IIv (ORCPT ); Sun, 28 Aug 2016 04:08:51 -0400 Received: from mail-it0-f67.google.com ([209.85.214.67]:35969 "EHLO mail-it0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755236AbcH1IIr (ORCPT ); Sun, 28 Aug 2016 04:08:47 -0400 MIME-Version: 1.0 In-Reply-To: <20160827022959.303563262@telegraphics.com.au> References: <20160827022958.983743612@telegraphics.com.au> <20160827022959.303563262@telegraphics.com.au> From: Geert Uytterhoeven Date: Sun, 28 Aug 2016 10:08:45 +0200 X-Google-Sender-Auth: agSBG__5h4yu_sSH_mIup4pfdA8 Message-ID: Subject: Re: [PATCH 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers To: Finn Thain Cc: "James E.J. Bottomley" , "Martin K. Petersen" , scsi , "Linux/m68k" , "linux-kernel@vger.kernel.org" , Michael Schmitz Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Finn, On Sat, Aug 27, 2016 at 4:30 AM, Finn Thain wrote: > Large PIO transfers are broken up into chunks to try to avoid disabling > local IRQs for long periods. But IRQs are still disabled for too long > and this causes SCC FIFO overruns during serial port transfers. This > patch fixes the problem by halving the PIO chunk size. > > Testing with mac_scsi shows that the extra NCR5380_main() loop iterations > have negligible performance impact on SCSI transfers (about 1% slower). > On a faster system (using the dmx3191d module) transfers showed no > measurable change. > > Signed-off-by: Finn Thain > > --- > drivers/scsi/NCR5380.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > Index: linux/drivers/scsi/NCR5380.c > =================================================================== > --- linux.orig/drivers/scsi/NCR5380.c 2016-08-27 12:29:57.000000000 +1000 > +++ linux/drivers/scsi/NCR5380.c 2016-08-27 12:29:58.000000000 +1000 > @@ -1847,11 +1847,11 @@ static void NCR5380_information_transfer > /* XXX - need to source or sink data here, as appropriate */ > } > } else { > - /* Break up transfer into 3 ms chunks, > - * presuming 6 accesses per handshake. > + /* Transfer a small chunk so that the > + * irq mode lock is not held too long. > */ > transfersize = min((unsigned long)cmd->SCp.this_residual, > - hostdata->accesses_per_ms / 2); > + hostdata->accesses_per_ms >> 2); I think it's easier to read if you use "/ 4". Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds