Re: [git] CFS-devel, latest code

Mike Galbraith
2007-09-25T13:35:29Z

On Tue, 2007-09-25 at 18:21 +0530, Srivatsa Vaddagiri wrote:
> 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.

http://lkml.org/lkml/2007/9/25/117 plus the below seems to be the SIlver
Bullet for the latencies I was seeing.

> 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;
> #endif
> - 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);
> }
>
>
> --
> Regards,
> vatsa