On Fri, Mar 11, 2011 at 11:56 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Fri, 11 Mar 2011, Scott James Remnant wrote: >> On Thu, Mar 10, 2011 at 12:25 AM, Andrew Morton >> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: >> > On Wed, 9 Mar 2011 18:01:09 -0800 Scott James Remnant <scott@xxxxxxxxxxxx> wrote: >> > >> >> > It would be helpful to know if the identified users of this feature >> >> > actually find it useful and adequate. __I guess the most common >> >> > application is the 1,001 desktop clock widgets. __Do you have any >> >> > feedback from any of the owners of those? >> >> > >> >> cron is another obvious one (or init systems attempting to replace >> >> cron). Having to wakeup and check the time every minute can be >> >> non-conducive to power savings, it would be better if we could just >> >> sleep until the next alarm and be woken up if the time changes in >> >> between. >> >> >> >> (That being said, we also need to poll for and/or check for timezone >> >> changes - but those are entirely userspace, so we can deal with that >> >> separately) >> > >> > Sure, there will be lots of applications. >> > >> > But what I'm asking isn't "it is a good feature". I'm asking "is the >> > feature implemented well". Ideally someone would get down and modify >> > cron to use the interface in this patch. >> > >> So I've just been thinking today - and I'm actually not sure whether >> this is needed at all for this case. >> >> A good cron implementation is going to set timers according to >> CLOCK_REALTIME; in the case where the clock changes forwards, those >> timers will fire as part of the clock changing already no? And in the >> case where the clock changes backwards, you don't want to re-run old >> ones anyway. >> >> Even the hourly/daily cases are actually at a fixed time, so would be >> triggered - and a decent implementation wouldn't trigger a given >> script more than once. > > Yeah, I was wondering about today as well. Though when you set back > your clock several days, stuff might be surprised if it's not woken up > for several days :) > I've checked the code, and more importantly, tested the setting-forward example - timers do indeed fire at the point the clock is wound forwards. This means there doesn't appear to be a utility for this patch in the cron case. In the wound back case, I believe that even current cron goes to some effort to avoid firing events that have already happened? Scott -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
