Messages in this thread | | | Date | Thu, 6 Mar 2014 23:41:46 +0100 | From | Andi Kleen <> | Subject | Re: [RFC] [PATCH] Pre-emption control for userspace |
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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
-- ak@linux.intel.com -- Speaking for myself only.
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