On Thu, Mar 06, 2014 at 02:59:46PM +0100, Peter Zijlstra wrote: > 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 you worry about fetching it you can always prefetch it early. > > 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). I guess it could be some predicted value, similar to how the menu governour works. -Andi -- [email protected] -- Speaking for myself only. -- 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/
