Commit 31915ab4 authored Sep 16, 2010 by Heiko Carstens Committed by Ingo Molnar Sep 16, 2010

sched: Remove branch hints within context_switch()



With 710390d9 "sched: Optimize branch hint in context_switch()"
the branch hint logic within context_switch() got inversed.

In fact the hints "if (likely(!mm))" and "if (likely(!prev->mm))"
mean that it is likely that the previous and next task are kernel
threads.

That assumption is certainly counter intuitive, but Tim has shown
that at least with his workload this is true. Nevertheless the
truth is: it depends on the current workload. So just remove the
annotations which also improves readability.

Reported-by: Tim Blechmann <tim@klingt.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20100916124225.GA2209@osiris.boeblingen.de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 7740191c

kernel/sched.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -2845,14 +2845,14 @@ context_switch(struct rq rq, struct task_struct prev,
	*/		*/
	arch_start_context_switch(prev);		arch_start_context_switch(prev);

	if (likely(!mm)) {		if (!mm) {
	next->active_mm = oldmm;		next->active_mm = oldmm;
	atomic_inc(&oldmm->mm_count);		atomic_inc(&oldmm->mm_count);
	enter_lazy_tlb(oldmm, next);		enter_lazy_tlb(oldmm, next);
	} else		} else
	switch_mm(oldmm, mm, next);		switch_mm(oldmm, mm, next);

	if (likely(!prev->mm)) {		if (!prev->mm) {
	prev->active_mm = NULL;		prev->active_mm = NULL;
	rq->prev_mm = oldmm;		rq->prev_mm = oldmm;
	}		}