On 04/17/2013 06:47 PM, zhang.y...@zte.com.cn wrote: > > > Darren Hart <dvh...@linux.intel.com> wrote on 2013/04/18 03:42:07: > >> >> >> On 04/17/2013 03:40 AM, zhang.y...@zte.com.cn wrote: >> > Darren Hart <dvh...@linux.intel.com> wrote on 2013/04/17 01:05:28: >> > >> > >> >> >> >> Performance isn't an issue here as this is an error path. The question >> >> is if the >> >> changed behavior will constitute a problem for existing applications. >> > Rather >> >> than a serialized cascading wake, we have them all wake at once. If an >> >> application depended on the first waker after owner death to do some >> > cleanup >> >> before the rest came along, I could imagine some potential for failure >> >> there. >> >> >> > >> > I don't find out there are any APIs can wake all waiters at once, so still >> > use futex_wake. >> > When waiter return form futex_wait syscall, glibc check the futex's value >> > and try to modify it by using atomic instructions, and let the waiter >> > return only if successed. >> > The applications which not use the glibc's library should follow this. >> >> Indeed they *should*. :-) >> >> > >> >> One possible alternative would be to wake waiters for a different >> >> process group >> >> when OWNER_DEAD is set, and leave it as a single wake. >> >> >> > >> > To wake one waiter of other process cannot slove this problem , because it >> > can be exiting too. >> >> If I understood the point of your change, it was to ensure all tasks >> would be woken because tasks that were exiting wouldn't propogate the >> wake. If there are nothing but exiting tasks available.... does it even >> matter? >> > > I mean that there may be some processes (more than 2) waitting for the > lock, we can't choose the one which is exiting or it will exit later. > It's difficult to accomplish this. >
"or it will exit later" .... I don't follow you there, it sounds like you are saying if we try to wake the exiting process, that process will be delayed and take longer to exit.... I don't think that is what you meant. Can you elaborate please? -- Darren Hart Intel Open Source Technology Center Yocto Project - Technical Lead - Linux Kernel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
