On Thu, Mar 06, 2014 at 11:13:33PM +1100, Kevin Easton wrote: > On Tue, Mar 04, 2014 at 04:51:15PM -0800, Andi Kleen wrote: > > Anything else? > > If it was possible to make the time remaining in the current timeslice > available to userspace through the vdso, the thread could do something like:
Assuming we can do per-cpu values in the VDSO; this would mean hitting that cacheline on every context switch and wakeup. That's a complete non-starter performance wise. > > if (sys_timeleft() < CRITICAL_SECTION_SIZE) > yield(); > lock(); > > to avoid running out of timeslice in the middle of the critical section. Can still happen, the effective slice of a single runnable task is infinite, the moment another task gets woken this gets reduced to a finite amount, we then keep reducing the slice until there are about 8 runnable tasks (assuming you've not poked at any sysctls). Also; depending on the state of the just woken task; it might land left of you in the tree, making it immediately eligible to run, completely obviating whatever number you just read. -- 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/
