Re: [git] CFS-devel, latest code

From: Srivatsa Vaddagiri
Date: Tue Sep 25 2007 - 08:41:18 EST

On Tue, Sep 25, 2007 at 12:36:17PM +0200, Ingo Molnar wrote:
> hm. perhaps this fixup in kernel/sched.c:set_task_cpu():
> p->se.vruntime -= old_rq->cfs.min_vruntime - new_rq->cfs.min_vruntime;

This definitely does need some fixup, even though I am not sure yet if
it will solve completely the latency issue.

I tried the following patch. I *think* I see some improvement, wrt
latency seen when I type on the shell. Before this patch, I noticed
oddities like "kill -9 chew-max-pid" wont kill chew-max (it is queued in
runqueue waiting for a looong time to run before it can acknowledge
signal and exit). With this patch, I don't see such oddities ..So I am hoping
it fixes the latency problem you are seeing as well.

Index: current/kernel/sched.c
--- current.orig/kernel/sched.c
+++ current/kernel/sched.c
@@ -1039,6 +1039,8 @@ void set_task_cpu(struct task_struct *p,
int old_cpu = task_cpu(p);
struct rq *old_rq = cpu_rq(old_cpu), *new_rq = cpu_rq(new_cpu);
+ struct cfs_rq *old_cfsrq = task_cfs_rq(p),
+ *new_cfsrq = cpu_cfs_rq(old_cfsrq, new_cpu);
u64 clock_offset;

clock_offset = old_rq->clock - new_rq->clock;
@@ -1051,7 +1053,8 @@ void set_task_cpu(struct task_struct *p,
if (p->se.block_start)
p->se.block_start -= clock_offset;
- p->se.vruntime -= old_rq->cfs.min_vruntime - new_rq->cfs.min_vruntime;
+ p->se.vruntime -= old_cfsrq->min_vruntime -
+ new_cfsrq->min_vruntime;

__set_task_cpu(p, new_cpu);

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