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From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: George Dunlap <george.dunlap@eu.citrix.com>,
	xen-devel@lists.xenproject.org,
	Dario Faggioli <dfaggioli@suse.com>
Subject: Re: [Xen-devel] [PATCH v2 27/48] xen/sched: Change vcpu_migrate_*() to operate on schedule unit
Date: Fri, 13 Sep 2019 14:33:25 +0200
Message-ID: <4224edef-ad3f-0b32-62e3-be3b90a40e85@suse.com> (raw)
In-Reply-To: <a33b4012-bef8-531f-6ddc-583ec76449a1@suse.com>

On 10.09.19 17:11, Jan Beulich wrote:
> On 09.08.2019 16:58, Juergen Gross wrote:
>> --- a/xen/common/schedule.c
>> +++ b/xen/common/schedule.c
>> @@ -733,35 +733,40 @@ void vcpu_unblock(struct vcpu *v)
>>   }
>>   
>>   /*
>> - * Do the actual movement of a vcpu from old to new CPU. Locks for *both*
>> + * Do the actual movement of an unit from old to new CPU. Locks for *both*
>>    * CPUs needs to have been taken already when calling this!
>>    */
>> -static void vcpu_move_locked(struct vcpu *v, unsigned int new_cpu)
>> +static void sched_unit_move_locked(struct sched_unit *unit,
>> +                                   unsigned int new_cpu)
>>   {
>> -    unsigned int old_cpu = v->processor;
>> +    unsigned int old_cpu = unit->res->processor;
>> +    struct vcpu *v;
>>   
>>       /*
>>        * Transfer urgency status to new CPU before switching CPUs, as
>>        * once the switch occurs, v->is_urgent is no longer protected by
>>        * the per-CPU scheduler lock we are holding.
>>        */
>> -    if ( unlikely(v->is_urgent) && (old_cpu != new_cpu) )
>> +    for_each_sched_unit_vcpu ( unit, v )
>>       {
>> -        atomic_inc(&get_sched_res(new_cpu)->urgent_count);
>> -        atomic_dec(&get_sched_res(old_cpu)->urgent_count);
>> +        if ( unlikely(v->is_urgent) && (old_cpu != new_cpu) )
>> +        {
>> +            atomic_inc(&get_sched_res(new_cpu)->urgent_count);
>> +            atomic_dec(&get_sched_res(old_cpu)->urgent_count);
>> +        }
>>       }
> 
> Shouldn't is_urgent become an attribute of unit rather than a vCPU,
> too, eliminating the need for a loop here? I can't see a reason
> why not, seeing this collapsing into a single urgent_count.

With moving urgent_count to a percpu variable this no longer applies.

> 
> Then again the question remains whether the non-deep sleeping as
> a result of a non-zero urgent_count should indeed be distributed
> to all constituents of a unit. I can see arguments both in favor
> and against.

Against has won. :-)

> 
>> -static void vcpu_migrate_finish(struct vcpu *v)
>> +static void sched_unit_migrate_finish(struct sched_unit *unit)
>>   {
>>       unsigned long flags;
>>       unsigned int old_cpu, new_cpu;
>>       spinlock_t *old_lock, *new_lock;
>>       bool_t pick_called = 0;
>> +    struct vcpu *v;
>>   
>>       /*
>> -     * If the vcpu is currently running, this will be handled by
>> +     * If the unit is currently running, this will be handled by
>>        * context_saved(); and in any case, if the bit is cleared, then
>>        * someone else has already done the work so we don't need to.
>>        */
>> -    if ( v->sched_unit->is_running ||
>> -         !test_bit(_VPF_migrating, &v->pause_flags) )
>> -        return;
>> +    for_each_sched_unit_vcpu ( unit, v )
>> +    {
>> +        if ( unit->is_running || !test_bit(_VPF_migrating, &v->pause_flags) )
>> +            return;
>> +    }
> 
> Do you really need the loop invariant unit->is_running to be evaluated
> once per loop iteration? (Same again further down at least once.)

No, I should test that before entering the loop.

> 
> Furthermore I wonder if VPF_migrating shouldn't become a per-unit
> attribute.

This would make vcpu_runnable() much more complicated. I don't think
that is worth it.

> 
>> @@ -858,22 +871,30 @@ static void vcpu_migrate_finish(struct vcpu *v)
>>        * because they both happen in (different) spinlock regions, and those
>>        * regions are strictly serialised.
>>        */
>> -    if ( v->sched_unit->is_running ||
>> -         !test_and_clear_bit(_VPF_migrating, &v->pause_flags) )
>> +    for_each_sched_unit_vcpu ( unit, v )
>>       {
>> -        sched_spin_unlock_double(old_lock, new_lock, flags);
>> -        return;
>> +        if ( unit->is_running ||
>> +             !test_and_clear_bit(_VPF_migrating, &v->pause_flags) )
>> +        {
>> +            sched_spin_unlock_double(old_lock, new_lock, flags);
>> +            return;
>> +        }
>>       }
>>   
>> -    vcpu_move_locked(v, new_cpu);
>> +    sched_unit_move_locked(unit, new_cpu);
>>   
>>       sched_spin_unlock_double(old_lock, new_lock, flags);
>>   
>>       if ( old_cpu != new_cpu )
>> -        sched_move_irqs(v->sched_unit);
>> +    {
>> +        for_each_sched_unit_vcpu ( unit, v )
>> +            sync_vcpu_execstate(v);
> 
> This is new without being explained anywhere. Or wait, it is mentioned
> (with the wrong function name, which is why initially - by searching -
> I didn't spot it), but only with a justification of "needed anyway".

I'll correct it and make it more verbose.

> 
>> @@ -1794,7 +1814,7 @@ void context_saved(struct vcpu *prev)
>>   
>>       sched_context_saved(vcpu_scheduler(prev), prev->sched_unit);
>>   
>> -    vcpu_migrate_finish(prev);
>> +    sched_unit_migrate_finish(prev->sched_unit);
>>   }
> 
> By the end of the series context_saved() still acts on vCPU-s, not
> units. What is the meaning/effect of multiple sched_unit_migrate_*()?

That's corrected in V3 by having split context_saved() into a vcpu- and
a unit-part.


Juergen

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Thread overview: 126+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-09 14:57 [Xen-devel] [PATCH v2 00/48] xen: add core scheduling support Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 01/48] xen/sched: use new sched_unit instead of vcpu in scheduler interfaces Juergen Gross
2019-09-02  9:07   ` Jan Beulich
2019-09-09  5:26     ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 02/48] xen/sched: move per-vcpu scheduler private data pointer to sched_unit Juergen Gross
2019-08-23 10:47   ` Dario Faggioli
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 03/48] xen/sched: build a linked list of struct sched_unit Juergen Gross
2019-08-23 10:52   ` Dario Faggioli
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 04/48] xen/sched: introduce struct sched_resource Juergen Gross
2019-08-23 10:54   ` Dario Faggioli
2019-09-04 13:10   ` Jan Beulich
2019-09-09  5:31     ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 05/48] xen/sched: let pick_cpu return a scheduler resource Juergen Gross
2019-09-04 13:34   ` Jan Beulich
2019-09-09  5:43     ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 06/48] xen/sched: switch schedule_data.curr to point at sched_unit Juergen Gross
2019-09-04 13:36   ` Jan Beulich
2019-09-09  5:46     ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 07/48] xen/sched: move per cpu scheduler private data into struct sched_resource Juergen Gross
2019-09-04 13:48   ` Jan Beulich
2019-09-05  7:13     ` Juergen Gross
2019-09-05  7:38       ` Jan Beulich
2019-09-09 13:03         ` Dario Faggioli
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 08/48] xen/sched: switch vcpu_schedule_lock to unit_schedule_lock Juergen Gross
2019-09-04 14:02   ` Jan Beulich
2019-09-04 14:41     ` Juergen Gross
2019-09-04 14:54       ` Jan Beulich
2019-09-04 15:02         ` Juergen Gross
2019-09-11 16:02           ` Dario Faggioli
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 09/48] xen/sched: move some per-vcpu items to struct sched_unit Juergen Gross
2019-09-04 14:16   ` Jan Beulich
2019-09-09  6:39     ` Juergen Gross
2019-09-09  6:55       ` Jan Beulich
2019-09-09  7:05         ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 10/48] xen/sched: add scheduler helpers hiding vcpu Juergen Gross
2019-09-04 14:49   ` Jan Beulich
2019-09-11 13:22     ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 11/48] xen/sched: rename scheduler related perf counters Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 12/48] xen/sched: switch struct task_slice from vcpu to sched_unit Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 13/48] xen/sched: add is_running indicator to struct sched_unit Juergen Gross
2019-09-04 15:06   ` Jan Beulich
2019-09-11 13:44     ` Juergen Gross
2019-09-11 15:06       ` Jan Beulich
2019-09-11 15:32         ` Juergen Gross
2019-08-09 14:57 ` [Xen-devel] [PATCH v2 14/48] xen/sched: make null scheduler vcpu agnostic Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 15/48] xen/sched: make rt " Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 16/48] xen/sched: make credit " Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 17/48] xen/sched: make credit2 " Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 18/48] xen/sched: make arinc653 " Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 19/48] xen: add sched_unit_pause_nosync() and sched_unit_unpause() Juergen Gross
2019-09-09 13:34   ` Jan Beulich
2019-09-11 14:15     ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 20/48] xen: let vcpu_create() select processor Juergen Gross
2019-08-23 16:42   ` Julien Grall
2019-09-09 13:38   ` Jan Beulich
2019-09-11 14:22     ` Juergen Gross
2019-09-11 17:20       ` Dario Faggioli
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 21/48] xen/sched: use sched_resource cpu instead smp_processor_id in schedulers Juergen Gross
2019-09-09 14:17   ` Jan Beulich
2019-09-12  9:34     ` Juergen Gross
2019-09-12 10:04       ` Jan Beulich
2019-09-12 11:03         ` Juergen Gross
2019-09-12 11:17         ` Juergen Gross
2019-09-12 11:46           ` Jan Beulich
2019-09-12 11:53             ` Juergen Gross
2019-09-12 12:08               ` Jan Beulich
2019-09-12 12:13                 ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 22/48] xen/sched: switch schedule() from vcpus to sched_units Juergen Gross
2019-09-09 14:35   ` Jan Beulich
2019-09-12 13:44     ` Juergen Gross
2019-09-12 14:34       ` Jan Beulich
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 23/48] xen/sched: switch sched_move_irqs() to take sched_unit as parameter Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 24/48] xen: switch from for_each_vcpu() to for_each_sched_unit() Juergen Gross
2019-09-09 15:14   ` Jan Beulich
2019-09-12 14:02     ` Juergen Gross
2019-09-12 14:40       ` Jan Beulich
2019-09-12 14:47         ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 25/48] xen/sched: add runstate counters to struct sched_unit Juergen Gross
2019-09-09 14:30   ` Jan Beulich
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 26/48] xen/sched: rework and rename vcpu_force_reschedule() Juergen Gross
2019-09-10 14:06   ` Jan Beulich
2019-09-13  9:33     ` Juergen Gross
2019-09-13  9:40       ` Jan Beulich
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 27/48] xen/sched: Change vcpu_migrate_*() to operate on schedule unit Juergen Gross
2019-09-10 15:11   ` Jan Beulich
2019-09-13 12:33     ` Juergen Gross [this message]
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 28/48] xen/sched: move struct task_slice into struct sched_unit Juergen Gross
2019-09-10 15:18   ` Jan Beulich
2019-09-13 12:56     ` Juergen Gross
2019-09-12  8:13   ` Dario Faggioli
2019-09-12  8:21     ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 29/48] xen/sched: add code to sync scheduling of all vcpus of a sched unit Juergen Gross
2019-09-10 15:36   ` Jan Beulich
2019-09-13 13:12     ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 30/48] xen/sched: introduce unit_runnable_state() Juergen Gross
2019-09-11 10:30   ` Jan Beulich
2019-09-12 10:22     ` Dario Faggioli
2019-09-13 14:07     ` Juergen Gross
2019-09-13 14:44       ` Jan Beulich
2019-09-13 15:23         ` Juergen Gross
2019-09-12 10:24   ` Dario Faggioli
2019-09-13 14:14     ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 31/48] xen/sched: add support for multiple vcpus per sched unit where missing Juergen Gross
2019-09-11 10:43   ` Jan Beulich
2019-09-13 15:01     ` Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 32/48] xen/sched: modify cpupool_domain_cpumask() to be an unit mask Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 33/48] xen/sched: support allocating multiple vcpus into one sched unit Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 34/48] xen/sched: add a percpu resource index Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 35/48] xen/sched: add fall back to idle vcpu when scheduling unit Juergen Gross
2019-09-11 11:33   ` Julien Grall
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 36/48] xen/sched: make vcpu_wake() and vcpu_sleep() core scheduling aware Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 37/48] xen/sched: carve out freeing sched_unit memory into dedicated function Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 38/48] xen/sched: move per-cpu variable scheduler to struct sched_resource Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 39/48] xen/sched: move per-cpu variable cpupool " Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 40/48] xen/sched: reject switching smt on/off with core scheduling active Juergen Gross
2019-09-10 15:47   ` Jan Beulich
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 41/48] xen/sched: prepare per-cpupool scheduling granularity Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 42/48] xen/sched: split schedule_cpu_switch() Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 43/48] xen/sched: protect scheduling resource via rcu Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 44/48] xen/sched: support multiple cpus per scheduling resource Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 45/48] xen/sched: support differing granularity in schedule_cpu_[add/rm]() Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 46/48] xen/sched: support core scheduling for moving cpus to/from cpupools Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 47/48] xen/sched: disable scheduling when entering ACPI deep sleep states Juergen Gross
2019-08-09 14:58 ` [Xen-devel] [PATCH v2 48/48] xen/sched: add scheduling granularity enum Juergen Gross
2019-08-15 10:17 ` [Xen-devel] [PATCH v2 00/48] xen: add core scheduling support Sergey Dyasli
2019-09-05  6:22   ` Juergen Gross

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