2016-08-17 9:54 GMT+08:00 Rik van Riel <riel@xxxxxxxxxx>: > On Wed, 2016-08-17 at 09:16 +0800, Wanpeng Li wrote: >> >> @@ -694,6 +699,12 @@ static cputime_t get_vtime_delta(struct >> task_struct *tsk) >> unsigned long now = READ_ONCE(jiffies); >> cputime_t delta, other; >> >> + /* >> + * The interval returned by account_other_time() is NOT >> + * rounded down to the nearest jiffy, while the base >> + * interval it is subtracted from is. So the max cputime >> + * limit is required to avoid underflow. >> + */ >> delta = jiffies_to_cputime(now - tsk->vtime_snap); >> other = account_other_time(delta); >> WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_INACTIVE); > > That comment makes sense in the context of the discussion > we have been having over the past few days, but could be > somewhat cryptic to someone looking at it 3 years from now. > > How about something like the following? > > /* > * Unlike tick based timing, vtime based timing never has lost > * ticks, and no need for steal time accounting to make up for > * lost ticks. Vtime accounts a rounded version of actual > * elapsed time. Limit account_other_time to prevent rounding > * errors from causing elapsed vtime to go negative. > */ Great, thanks for your help. I will send out a new version soon. :) Regards, Wanpeng Li -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
