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From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Tim Deegan <tim@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Robert VanVossen <robert.vanvossen@dornerworks.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	Julien Grall <julien.grall@arm.com>,
	Josh Whitehead <josh.whitehead@dornerworks.com>,
	Meng Xu <mengxu@cis.upenn.edu>,
	xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH v2 21/48] xen/sched: use sched_resource cpu instead smp_processor_id in schedulers
Date: Thu, 12 Sep 2019 13:03:03 +0200
Message-ID: <2118ba75-6f4f-89e8-3d16-b624617b70ab@suse.com> (raw)
In-Reply-To: <5aeddfeb-e01f-2cef-59ff-d66bcc067d37@suse.com>

On 12.09.19 12:04, Jan Beulich wrote:
> On 12.09.2019 11:34, Juergen Gross wrote:
>> On 09.09.19 16:17, Jan Beulich wrote:
>>> On 09.08.2019 16:58, Juergen Gross wrote:
>>>> @@ -1825,8 +1825,9 @@ static struct task_slice
>>>>    csched_schedule(
>>>>        const struct scheduler *ops, s_time_t now, bool_t tasklet_work_scheduled)
>>>>    {
>>>> -    const int cpu = smp_processor_id();
>>>> -    struct list_head * const runq = RUNQ(cpu);
>>>> +    const unsigned int cpu = smp_processor_id();
>>>> +    const unsigned int sched_cpu = sched_get_resource_cpu(cpu);
>>>> +    struct list_head * const runq = RUNQ(sched_cpu);
>>>
>>> By retaining a local variable named "cpu" you make it close to
>>> impossible to notice, during a re-base, an addition to the
>>> function still referencing a variable of this name. Similarly
>>> review is being made harder because one needs to go hunt all
>>> the remaining uses of "cpu". For example there a trace entry
>>> being generated, and it's not obvious to me whether this wouldn't
>>> better also used sched_cpu.
>>
>> Okayy, I'll rename "cpu" to "my_cpu".
> 
> We've got a number of instances of "this_cpu" in such cases already,
> but no single "my_cpu". May I suggest to stick to this naming here
> as well?
> 
>> I used cpu in the trace entry on purpose, as it might be interesting on
>> which cpu the entry has been produced.
> 
> Right, that's how I understood it; it simply seemed like there
> might be a similarly valid view to the contrary.
> 
>>>> @@ -1967,7 +1968,7 @@ csched_schedule(
>>>>        if ( snext->pri > CSCHED_PRI_TS_OVER )
>>>>            __runq_remove(snext);
>>>>        else
>>>> -        snext = csched_load_balance(prv, cpu, snext, &ret.migrated);
>>>> +        snext = csched_load_balance(prv, sched_cpu, snext, &ret.migrated);
>>>
>>> And in a case like this one I wonder whether passing a "sort of
>>> CPU" isn't sufficiently confusing, compared to e.g. simply
>>> passing the corresponding unit.
>>
>> I guess you mean sched_resource.
> 
> Not sure - with scheduling acting on units, it would seem to me that
> passing around the unit pointers would be the most appropriate thing.
> 
>> I don't think changing the parameter type is a good idea. We need both
>> (resource and cpu number) on caller and callee side, but the main
>> object csched_load_balance() is working on is the cpu number.
> 
> I see. Part of my thinking here also was towards the added type
> safety if passing pointers instead of numeric values.
> 
>>>> @@ -1975,12 +1976,12 @@ csched_schedule(
>>>>         */
>>>>        if ( !tasklet_work_scheduled && snext->pri == CSCHED_PRI_IDLE )
>>>>        {
>>>> -        if ( !cpumask_test_cpu(cpu, prv->idlers) )
>>>> -            cpumask_set_cpu(cpu, prv->idlers);
>>>> +        if ( !cpumask_test_cpu(sched_cpu, prv->idlers) )
>>>> +            cpumask_set_cpu(sched_cpu, prv->idlers);
>>>>        }
>>>> -    else if ( cpumask_test_cpu(cpu, prv->idlers) )
>>>> +    else if ( cpumask_test_cpu(sched_cpu, prv->idlers) )
>>>>        {
>>>> -        cpumask_clear_cpu(cpu, prv->idlers);
>>>> +        cpumask_clear_cpu(sched_cpu, prv->idlers);
>>>>        }
>>>
>>> And this looks to be a pretty gross abuse of CPU masks then.
>>> (Nevertheless I can see that using a CPU as a vehicle here is
>>> helpful to limit the scope of the already long series, but I
>>> think it needs to be made much more apparent what is meant.)
>>
>> I don't think it is an abuse. Think of it as a cpumask where only
>> the bits related to the resource's master_cpus can be set.
> 
> Well, I understand that this was your thinking behind retaining
> the use of CPU masks here. With the "master_cpu" naming it may
> indeed end up looking less abuse-like, but I still wonder (as
> also suggested elsewhere) whether an ID concept similar to that
> of APIC ID vs (derived) core/socket/node ID wouldn't be better
> in cases where an ID is to represent multiple CPUs.

Thinking of a future support of cpupools with different scheduling
granularity I don't think this is a good idea. The only way to not
letting that become rather awful would be to let the ID have the
same numerical value as the cpu today and duplicate the cpumask
stuff into a resourcemask framework compoletely the same but with
different names.


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 [this message]
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
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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