[Xen-users] xen credit

[张伟 <zhangwqh@xxxxxxx>]

Hi all,

Now I am reading the source code sched-credit. The xen version is 4.2.1.  I can not fully understand two places.

One place is:

There is a variable in schedule.c. There is per cpu variable, tasklet_work_to_do. Read this variable, set the tasklet_work, 

unsigned long        *tasklet_work = &this_cpu(tasklet_work_to_do);

    bool_t                tasklet_work_scheduled = 0;

Then according to the task_work, set the tasklet_work_scheduled:

/* Update tasklet scheduling status. */

    switch ( *tasklet_work )

    {

    case TASKLET_enqueued:

        set_bit(_TASKLET_scheduled, tasklet_work);

    case TASKLET_enqueued|TASKLET_scheduled:

        tasklet_work_scheduled = 1;

        break;

    case TASKLET_scheduled:

        clear_bit(_TASKLET_scheduled, tasklet_work);

    case 0:

        /*tasklet_work_scheduled = 0;*/

        break;

    default:

        BUG();

    }

I can not understand the function of tasklet_work_to_do, tasklet_work, tasklet_work_scheduled. I can not understand  their meaning. In the sched_credit.c file, 

there are two places that use tasklet_work_scheduled. I can not understand the meaning of tasklet_work_scheduled.

One place:

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;

}

the other place:

if ( tasklet_work_scheduled )

    {

        snext = CSCHED_VCPU(idle_vcpu[cpu]);

        snext->pri = CSCHED_PRI_TS_BOOST;

    }

This variable tasklet_work_scheduled is obstacle I understand the source code.

Other question is the member s_time_t start_time in structure struct csched_vcpu. The meaning and function for this variable?

I do not know why when a vcpu is descheduled, its start_time - now, why a vcpu is scheduled, its start_time + now?

deschedule:

if ( !is_idle_vcpu(scurr->vcpu) )

    {

        /* Update credits of a non-idle VCPU. */

        burn_credits(scurr, now);

        scurr->start_time -= now;

    }

schedule:

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;

    }

Anybody can give me some advice for these problems? Thank you in advance!

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxx
http://lists.xen.org/xen-users