On Mon, 2008-02-18 at 13:50 +0530, Srivatsa Vaddagiri wrote:
> On Mon, Feb 18, 2008 at 08:38:24AM +0100, Mike Galbraith wrote:
> > Here, it does not. It seems fine without CONFIG_FAIR_GROUP_SCHED.
>
> My hunch is its because of the vruntime driven preemption which shoots
> up latencies (and the fact perhaps that Peter hasnt't focused more on SMP case
> yet!).
>
> Curiously, do you observe the same results when in UP mode (maxcpus=1)?
No, I only see bad latency with SMP.
> FWIW, my test patch I had sent earlier didnt address the needs of UP, as
> Peter
> pointed me out. In that direction, I had done more experimentation with the
> patch below, which seemed to improve UP latencies also. Note that I
> don't particularly like the first hunk below, perhaps it needs to be
> surrounded by an if(something) ..
I'll try this patch later (errands).
Thanks,
-Mike
>
> ---
> kernel/sched_fair.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> Index: current/kernel/sched_fair.c
> ===================================================================
> --- current.orig/kernel/sched_fair.c
> +++ current/kernel/sched_fair.c
> @@ -523,8 +523,6 @@ place_entity(struct cfs_rq *cfs_rq, stru
> if (sched_feat(NEW_FAIR_SLEEPERS))
> vruntime -= sysctl_sched_latency;
>
> - /* ensure we never gain time by being placed backwards. */
> - vruntime = max_vruntime(se->vruntime, vruntime);
> }
>
> se->vruntime = vruntime;
> @@ -816,6 +814,13 @@ hrtick_start_fair(struct rq *rq, struct
> }
> #endif
>
> +static inline void dequeue_stack(struct sched_entity *se)
> +{
> + for_each_sched_entity(se)
> + if (se->on_rq)
> + dequeue_entity(cfs_rq_of(se), se, 0);
> +}
> +
> /*
> * The enqueue_task method is called before nr_running is
> * increased. Here we update the fair scheduling stats and
> @@ -828,6 +833,9 @@ static void enqueue_task_fair(struct rq
> *topse = NULL; /* Highest schedulable entity */
> int incload = 1;
>
> + if (wakeup)
> + dequeue_stack(se);
> +
> for_each_sched_entity(se) {
> topse = se;
> if (se->on_rq) {
>
>
>
> P.S : Sorry about slow responses, since I am now in a different project :(
>
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