From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755091AbbKYDRY (ORCPT ); Tue, 24 Nov 2015 22:17:24 -0500 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:46922 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754248AbbKYDRU (ORCPT ); Tue, 24 Nov 2015 22:17:20 -0500 Date: Wed, 25 Nov 2015 14:17:09 +1100 (AEDT) From: Finn Thain To: Ondrej Zary cc: "James E.J. Bottomley" , Michael Schmitz , linux-m68k@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 22/71] ncr5380: Eliminate selecting state In-Reply-To: <201511242008.35378.linux@rainbow-software.org> Message-ID: References: <20151118083455.331768508@telegraphics.com.au> <20151118083501.571002212@telegraphics.com.au> <201511242008.35378.linux@rainbow-software.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 24 Nov 2015, Ondrej Zary wrote: > On Wednesday 18 November 2015 09:35:17 Finn Thain wrote: > > Linux v2.1.105 changed the algorithm for polling for the BSY signal > > in NCR5380_select() and NCR5380_main(). > > > > Presently, this code has a bug. Back then, NCR5380_set_timer(hostdata, 1) > > meant reschedule main() after sleeping for 10 ms. Repeated 25 times this > > provided the recommended 250 ms selection time-out delay. This got broken > > when HZ became configurable. > > > > We could fix this but there's no need to reschedule the main loop. This > > BSY polling presently happens when the NCR5380_main() work queue item > > calls NCR5380_select(), which in turn schedules NCR5380_main(), which > > calls NCR5380_select() again, and so on. > > > > This algorithm is a deviation from the simpler one in atari_NCR5380.c. > > The extra complexity and state is pointless. There's no reason to > > stop selection half-way and return to to the main loop when the main > > loop can do nothing useful until selection completes. > > > > So just poll for BSY. We can sleep while polling now that we have a > > suitable workqueue. > > Bisecting slow module initialization pointed to this commit. That's disappointing. This patch removed some nasty code. Anyway, thanks for taking the trouble to bisect. > > Before this commit (2 seconds): > [ 60.317374] scsi host2: Generic NCR5380/NCR53C400 SCSI, io_port 0x0, n_io_port 0, base 0xd8000, irq 0, can_queue 16, cmd_per_lun 2, sg_tablesize 128, this_id 7, flags { NCR53C400 }, USLEEP_POLL 3, USLEEP_SLEEP 50, options { AUTOPROBE_IRQ PSEUDO_DMA } > [ 60.780715] scsi 2:0:1:0: Direct-Access QUANTUM LP240S GM240S01X 4.6 PQ: 0 ANSI: 2 CCS > [ 62.606260] sd 2:0:1:0: Attached scsi generic sg1 type 0 > > > After this commit (22 seconds): > [ 137.511711] scsi host2: Generic NCR5380/NCR53C400 SCSI, io_port 0x0, n_io_port 0, base 0xd8000, irq 0, can_queue 16, cmd_per_lun 2, sg_tablesize 128, this_id 7, flags { NCR53C400 }, USLEEP_POLL 3, USLEEP_SLEEP 50, options { AUTOPROBE_IRQ PSEUDO_DMA } > [ 145.028532] clocksource: timekeeping watchdog: Marking clocksource 'tsc' as unstable because the skew is too large: > [ 145.029767] clocksource: 'acpi_pm' wd_now: a49738 wd_last: f4da04 mask: ffffff > [ 145.029828] clocksource: 'tsc' cs_now: 2ea624698e cs_last: 2c710aa17f mask: ffffffffffffffff > [ 145.032733] clocksource: Switched to clocksource acpi_pm I figured that it was okay to sleep from an unbound CPU-intensive workqueue but doing so seems to cause problems. (See also patch 66/71 "Fix soft lockups".) Perhaps a kthread is needed instead of a workqueue? (This workqueue already has it's own kthread, but top shows that it doesn't accrue CPU time.) > [ 145.236951] scsi 2:0:1:0: Direct-Access QUANTUM LP240S GM240S01X 4.6 PQ: 0 ANSI: 2 CCS > [ 159.959308] sd 2:0:1:0: Attached scsi generic sg1 type 0 > > This problem doesn't show up on my hardware, and I'd like to know where those 22 seconds are being spent. Would you please apply the entire series and add, #define NDEBUG (NDEBUG_ARBITRATION | NDEBUG_SELECTION | NDEBUG_MAIN) to the top of g_NCR5380.c and send me the messages logged during modprobe? --