Re: [Xen-devel] [PATCH] xen/sched_credit: Use delay to control scheduling frequency

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Mon, Jan 9, 2012 at 10:22 AM, Hui Lv <hui.lv@xxxxxxxxx> wrote:
> Updated the warning sentence for ratelimit_us.
>
> This patch can improve Xen performance:
> 1. Basically, the "delay method" can achieve 11% overall performance boost 
> for SPECvirt than original credit scheduler.
> 2. We have tried 1ms delay and 10ms delay, there is no big difference between 
> these two configurations. (1ms is enough to achieve a good performance)
> 3. We have compared different load level response time/latency (low, high, 
> peak), "delay method" didn't bring very much response time increase.
> 4. 1ms delay can reduce 30% context switch at peak performance, where 
> produces the benefits. (int sched_ratelimit_us = 1000 is the recommended 
> setting)
>
> Signed-off-by: Hui Lv <hui.lv@xxxxxxxxx>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>
> Acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

Just confirming this:
Acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

Thanks, Hui.
 -George

>
> diff -r a4bff36780a3 -r fe8d0ca867aa xen/common/sched_credit.c
> --- a/xen/common/sched_credit.c Fri Dec 16 18:46:27 2011 +0000
> +++ b/xen/common/sched_credit.c Mon Jan 09 05:21:35 2012 -0500
> @@ -172,6 +172,7 @@ struct csched_private {
>     uint32_t credit;
>     int credit_balance;
>     uint32_t runq_sort;
> +    unsigned ratelimit_us;
>     /* Period of master and tick in milliseconds */
>     unsigned tslice_ms, tick_period_us, ticks_per_tslice;
>     unsigned credits_per_tslice;
> @@ -1297,10 +1298,15 @@ csched_schedule(
>     struct csched_private *prv = CSCHED_PRIV(ops);
>     struct csched_vcpu *snext;
>     struct task_slice ret;
> +    s_time_t runtime, tslice;
>
>     CSCHED_STAT_CRANK(schedule);
>     CSCHED_VCPU_CHECK(current);
>
> +    runtime = now - current->runstate.state_entry_time;
> +    if ( runtime < 0 ) /* Does this ever happen? */
> +        runtime = 0;
> +
>     if ( !is_idle_vcpu(scurr->vcpu) )
>     {
>         /* Update credits of a non-idle VCPU. */
> @@ -1313,6 +1319,35 @@ csched_schedule(
>         scurr->pri = CSCHED_PRI_IDLE;
>     }
>
> +    /* Choices, choices:
> +     * - If we have a tasklet, we need to run the idle vcpu no matter what.
> +     * - If sched rate limiting is in effect, and the current vcpu has
> +     *   run for less than that amount of time, continue the current one,
> +     *   but with a shorter timeslice and return it immediately
> +     * - Otherwise, chose the one with the highest priority (which may
> +     *   be the one currently running)
> +     * - If the currently running one is TS_OVER, see if there
> +     *   is a higher priority one waiting on the runqueue of another
> +     *   cpu and steal it.
> +     */
> +
> +    /* If we have schedule rate limiting enabled, check to see
> +     * how long we've run for. */
> +    if ( !tasklet_work_scheduled
> +         && prv->ratelimit_us
> +         && vcpu_runnable(current)
> +         && !is_idle_vcpu(current)
> +         && runtime < MICROSECS(prv->ratelimit_us) )
> +    {
> +        snext = scurr;
> +        snext->start_time += now;
> +        perfc_incr(delay_ms);
> +        tslice = MICROSECS(prv->ratelimit_us);
> +        ret.migrated = 0;
> +        goto out;
> +    }
> +    tslice = MILLISECS(prv->tslice_ms);
> +
>     /*
>      * Select next runnable local VCPU (ie top of local runq)
>      */
> @@ -1367,11 +1402,12 @@ csched_schedule(
>     if ( !is_idle_vcpu(snext->vcpu) )
>         snext->start_time += now;
>
> +out:
>     /*
>      * Return task to run next...
>      */
>     ret.time = (is_idle_vcpu(snext->vcpu) ?
> -                -1 : MILLISECS(prv->tslice_ms));
> +                -1 : tslice);
>     ret.task = snext->vcpu;
>
>     CSCHED_VCPU_CHECK(ret.task);
> @@ -1533,6 +1569,15 @@ csched_init(struct scheduler *ops)
>     prv->tick_period_us = prv->tslice_ms * 1000 / prv->ticks_per_tslice;
>     prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv->tslice_ms;
>
> +    if ( MICROSECS(sched_ratelimit_us) > MILLISECS(sched_credit_tslice_ms) )
> +    {
> +        printk("WARNING: sched_ratelimit_us >"
> +               "sched_credit_tslice_ms is undefined\n"
> +               "Setting ratelimit_us to 1000 * tslice_ms\n");
> +        prv->ratelimit_us = 1000 * prv->tslice_ms;
> +    }
> +    else
> +        prv->ratelimit_us = sched_ratelimit_us;
>     return 0;
>  }
>
> diff -r a4bff36780a3 -r fe8d0ca867aa xen/common/schedule.c
> --- a/xen/common/schedule.c     Fri Dec 16 18:46:27 2011 +0000
> +++ b/xen/common/schedule.c     Mon Jan 09 05:21:35 2012 -0500
> @@ -47,6 +47,11 @@ string_param("sched", opt_sched);
>  bool_t sched_smt_power_savings = 0;
>  boolean_param("sched_smt_power_savings", sched_smt_power_savings);
>
> +/* Default scheduling rate limit: 1ms
> + * The behavior when sched_ratelimit_us is greater than 
> sched_credit_tslice_ms is undefined
> + * */
> +int sched_ratelimit_us = 1000;
> +integer_param("sched_ratelimit_us", sched_ratelimit_us);
>  /* Various timer handlers. */
>  static void s_timer_fn(void *unused);
>  static void vcpu_periodic_timer_fn(void *data);
> diff -r a4bff36780a3 -r fe8d0ca867aa xen/include/xen/perfc_defn.h
> --- a/xen/include/xen/perfc_defn.h      Fri Dec 16 18:46:27 2011 +0000
> +++ b/xen/include/xen/perfc_defn.h      Mon Jan 09 05:21:35 2012 -0500
> @@ -16,6 +16,7 @@ PERFCOUNTER(sched_irq,              "sch
>  PERFCOUNTER(sched_run,              "sched: runs through scheduler")
>  PERFCOUNTER(sched_ctx,              "sched: context switches")
>
> +PERFCOUNTER(delay_ms,               "csched: delay")
>  PERFCOUNTER(vcpu_check,             "csched: vcpu_check")
>  PERFCOUNTER(schedule,               "csched: schedule")
>  PERFCOUNTER(acct_run,               "csched: acct_run")
> diff -r a4bff36780a3 -r fe8d0ca867aa xen/include/xen/sched-if.h
> --- a/xen/include/xen/sched-if.h        Fri Dec 16 18:46:27 2011 +0000
> +++ b/xen/include/xen/sched-if.h        Mon Jan 09 05:21:35 2012 -0500
> @@ -16,6 +16,11 @@ extern struct cpupool *cpupool0;
>  /* cpus currently in no cpupool */
>  extern cpumask_t cpupool_free_cpus;
>
> +/* Scheduler generic parameters
> + * */
> +extern int sched_ratelimit_us;
> +
> +
>  /*
>  * In order to allow a scheduler to remap the lock->cpu mapping,
>  * we have a per-cpu pointer, along with a pre-allocated set of
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

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