From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753998AbaGUIhn (ORCPT ); Mon, 21 Jul 2014 04:37:43 -0400 Received: from cantor2.suse.de ([195.135.220.15]:44942 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753981AbaGUIhm (ORCPT ); Mon, 21 Jul 2014 04:37:42 -0400 Subject: Re: [patch V2 40/64] hwmon: ibmaem: Use ktime_get_ns() From: Jean Delvare To: Thomas Gleixner , "Darrick J. Wong" Cc: LKML , John Stultz , Peter Zijlstra In-Reply-To: <20140716205055.584960520@linutronix.de> References: <20140716205018.175419210@linutronix.de> <20140716205055.584960520@linutronix.de> Content-Type: text/plain; charset="UTF-8" Organization: Suse Linux Date: Mon, 21 Jul 2014 10:37:38 +0200 Message-ID: <1405931858.4939.30.camel@chaos.site> Mime-Version: 1.0 X-Mailer: Evolution 2.28.2 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, Le Wednesday 16 July 2014 à 21:04 +0000, Thomas Gleixner a écrit : > Using the wall clock time for delta time calculations is wrong to > begin with because wall clock time can be set from userspace and NTP. > Such data wants to be based on clock monotonic. > > The calcuations also are done on a nanosecond basis. Use the Typo: calculations > nanoseconds based interface right away. > > Signed-off-by: Thomas Gleixner > Cc: Jean Delvare > --- > drivers/hwmon/ibmaem.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > Index: tip/drivers/hwmon/ibmaem.c > =================================================================== > --- tip.orig/drivers/hwmon/ibmaem.c > +++ tip/drivers/hwmon/ibmaem.c > @@ -842,11 +842,10 @@ static ssize_t aem_show_power(struct dev > struct aem_data *data = dev_get_drvdata(dev); > u64 before, after, delta, time; > signed long leftover; > - struct timespec b, a; > > mutex_lock(&data->lock); > update_aem_energy_one(data, attr->index); > - getnstimeofday(&b); > + time = ktime_get_ns(); > before = data->energy[attr->index]; > > leftover = schedule_timeout_interruptible( > @@ -858,11 +857,10 @@ static ssize_t aem_show_power(struct dev > } > > update_aem_energy_one(data, attr->index); > - getnstimeofday(&a); > + time = ktime_get_ns() - time; > after = data->energy[attr->index]; > mutex_unlock(&data->lock); > > - time = timespec_to_ns(&a) - timespec_to_ns(&b); > delta = (after - before) * UJ_PER_MJ; > > return sprintf(buf, "%llu\n", I'm not familiar with the driver and I can't test it, and I'm not familiar with kernel timekeeping either. All I can say is that the changes look reasonable and good. Acked-by: Jean Delvare Darrick, maybe you want to comment or test? -- Jean Delvare SUSE L3 Support