From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751238AbdAMUPK (ORCPT ); Fri, 13 Jan 2017 15:15:10 -0500 Received: from 92-243-34-74.adsl.nanet.at ([92.243.34.74]:52058 "EHLO mail.osadl.at" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751117AbdAMUPI (ORCPT ); Fri, 13 Jan 2017 15:15:08 -0500 Date: Fri, 13 Jan 2017 20:14:30 +0000 From: Nicholas Mc Guire To: Dmitry Torokhov Cc: Nicholas Mc Guire , Henrik Rydberg , Dudley Du , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] Input: cyapa: use time based retry loop Message-ID: <20170113201430.GA3063@osadl.at> References: <1484337456-32596-1-git-send-email-hofrat@osadl.org> <20170113200745.GA8652@dtor-ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170113200745.GA8652@dtor-ws> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 13, 2017 at 12:07:45PM -0800, Dmitry Torokhov wrote: > On Fri, Jan 13, 2017 at 08:57:36PM +0100, Nicholas Mc Guire wrote: > > Using counter based retry loops for peripherals results in the delay > > being significantly overrun during high-load situations where delay > > functions tend to be vary imprecise and overrun there timeouts. So > > condition the termination on the actual condition of 2s for the > > re-calibration to have been successful. > > > > As this is a very long delay there is no advantage in using > > high-resolution timers thus switching this to msleep(). > > > > Signed-off-by: Nicholas Mc Guire > > --- > > Problem detected with coccinelle script (usleep_range for long delay) > > > > The basic model for the fix up here is to use > > > > timeout = jiffies + (retry_time) > > do { > > check() > > mleep() > > } while (time_is_after_jiffies(timeout)); > > > > rather than using a counter and have very long retry loops under load > > conditions. In the specific case it is sleep()/check() though to wait > > on the previous write to complete. The initial intent was to move the > > usleep_range() to msleep() as the delays are very long - if this > > refactoring of the timeout loop is desirable or not is not clear (both > > time and count based models seem to be common). > > > > Patch was compile tested with: x86_64_defconfig + CONFIG_MOUSE_CYAPA=m > > > > Patch is against 4.10-rc3 (localversion-next is next-20170113) > > > > drivers/input/mouse/cyapa_gen3.c | 27 ++++++++++++--------------- > > 1 file changed, 12 insertions(+), 15 deletions(-) > > > > diff --git a/drivers/input/mouse/cyapa_gen3.c b/drivers/input/mouse/cyapa_gen3.c > > index f9600753..0c544de 100644 > > --- a/drivers/input/mouse/cyapa_gen3.c > > +++ b/drivers/input/mouse/cyapa_gen3.c > > @@ -789,7 +789,7 @@ static ssize_t cyapa_gen3_do_calibrate(struct device *dev, > > const char *buf, size_t count) > > { > > struct cyapa *cyapa = dev_get_drvdata(dev); > > - int tries; > > + unsigned long timeout; > > int ret; > > > > ret = cyapa_read_byte(cyapa, CYAPA_CMD_DEV_STATUS); > > @@ -812,31 +812,28 @@ static ssize_t cyapa_gen3_do_calibrate(struct device *dev, > > goto out; > > } > > > > - tries = 20; /* max recalibration timeout 2s. */ > > + /* max recalibration timeout 2s. */ > > + timeout = jiffies + 20 * HZ; > > Doesn't this make timeout 20 sec instead of 2? yes - my bad - that should have been 2 > > > do { > > /* > > * For this recalibration, the max time will not exceed 2s. > > * The average time is approximately 500 - 700 ms, and we > > * will check the status every 100 - 200ms. > > */ > > - usleep_range(100000, 200000); > > - > > + msleep(100); > > ret = cyapa_read_byte(cyapa, CYAPA_CMD_DEV_STATUS); > > if (ret < 0) { > > - dev_err(dev, "Error reading dev status: %d\n", > > - ret); > > + dev_err(dev, "Error reading dev status: %d\n", ret); > > goto out; > > } > > - if ((ret & CYAPA_DEV_NORMAL) == CYAPA_DEV_NORMAL) > > - break; > > - } while (--tries); > > + if ((ret & CYAPA_DEV_NORMAL) == CYAPA_DEV_NORMAL) { > > + dev_dbg(dev, "Calibration successful.\n"); > > + goto out; > > + } > > + } while (time_is_after_jiffies(timeout)); > > > > - if (tries == 0) { > > - dev_err(dev, "Failed to calibrate. Timeout.\n"); > > - ret = -ETIMEDOUT; > > - goto out; > > - } > > - dev_dbg(dev, "Calibration successful.\n"); > > + dev_err(dev, "Failed to calibrate. Timeout.\n"); > > + ret = -ETIMEDOUT; > > > > out: > > return ret < 0 ? ret : count; > > -- > > 2.1.4 > > > > -- > Dmitry