On Mon, Jul 21, 2014 at 10:37:38AM +0200, Jean Delvare wrote: > 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 <[email protected]> > > Cc: Jean Delvare <[email protected]> > > --- > > 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 <[email protected]> > > Darrick, maybe you want to comment or test?
Looks ok to me from a theoretical point of view, but since I no longer work at IBM, I don't have hardware for a real test. :( --D > > -- > Jean Delvare > SUSE L3 Support > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
