Commit 46151122 authored May 08, 2008 by Mike Galbraith Committed by Ingo Molnar May 08, 2008

sched: fix weight calculations



The conversion between virtual and real time is as follows:

  dvt = rw/w * dt <=> dt = w/rw * dvt

Since we want the fair sleeper granularity to be in real time, we actually
need to do:

  dvt = - rw/w * l

This bug could be related to the regression reported by Yanmin Zhang:

| Comparing with kernel 2.6.25, sysbench+mysql(oltp, readonly) has lots
| of regressions with 2.6.26-rc1:
|
| 1) 8-core stoakley: 28%;
| 2) 16-core tigerton: 20%;
| 3) Itanium Montvale: 50%.

Reported-by: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent bf726eab

kernel/sched_fair.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -662,10 +662,15 @@ place_entity(struct cfs_rq cfs_rq, struct sched_entity se, int initial)
		if (!initial) {
		/* sleeps upto a single latency don't count. */
		if (sched_feat(NEW_FAIR_SLEEPERS)) {
		unsigned long thresh = sysctl_sched_latency;

		/*
		* convert the sleeper threshold into virtual time
		*/
		if (sched_feat(NORMALIZED_SLEEPER))
		vruntime -= calc_delta_weight(sysctl_sched_latency, se);
		else
		vruntime -= sysctl_sched_latency;
		thresh = calc_delta_fair(thresh, se);

		vruntime -= thresh;
		}

		/* ensure we never gain time by being placed backwards. */