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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>,
	"Dario Faggioli" <dfaggioli@suse.com>,
	"Julien Grall" <julien.grall@arm.com>,
	xen-devel@lists.xenproject.org,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v2 29/48] xen/sched: add code to sync scheduling of all vcpus of a sched unit
Date: Fri, 13 Sep 2019 15:12:27 +0200
Message-ID: <0a38b0cf-cc53-a672-f5ce-52169335f59c@suse.com> (raw)
In-Reply-To: <8d1e2ee8-a80f-2aa8-d10e-c549439bac87@suse.com>

On 10.09.19 17:36, Jan Beulich wrote:
> On 09.08.2019 16:58, Juergen Gross wrote:
>> +static bool sched_tasklet_check(unsigned int cpu)
>> +{
>> +    bool tasklet_work_scheduled = false;
>> +    const cpumask_t *mask = get_sched_res(cpu)->cpus;
>> +    int cpu_iter;
> 
> unsigned int ?

Yes.

> 
>> +static void context_saved(struct vcpu *prev)
>> +{
>> +    struct sched_unit *unit = prev->sched_unit;
>> +
>> +    /* Clear running flag /after/ writing context to memory. */
>> +    smp_wmb();
>> +
>> +    prev->is_running = 0;
>> +    unit->is_running = 0;
>> +    unit->state_entry_time = NOW();
>> +
>> +    /* Check for migration request /after/ clearing running flag. */
>> +    smp_mb();
>> +
>> +    sched_context_saved(vcpu_scheduler(prev), unit);
>> +
>> +    sched_unit_migrate_finish(unit);
>> +}
>> +
>> +/*
>> + * Rendezvous on end of context switch.
>> + * As no lock is protecting this rendezvous function we need to use atomic
>> + * access functions on the counter.
>> + * The counter will be 0 in case no rendezvous is needed. For the rendezvous
>> + * case it is initialised to the number of cpus to rendezvous plus 1. Each
>> + * member entering decrements the counter. The last one will decrement it to
>> + * 1 and perform the final needed action in that case (call of context_saved()
>> + * if vcpu was switched), and then set the counter to zero. The other members
>> + * will wait until the counter becomes zero until they proceed.
>> + */
>> +void sched_context_switched(struct vcpu *vprev, struct vcpu *vnext)
>> +{
>> +    struct sched_unit *next = vnext->sched_unit;
>> +
>> +    if ( atomic_read(&next->rendezvous_out_cnt) )
>> +    {
>> +        int cnt = atomic_dec_return(&next->rendezvous_out_cnt);
>> +
>> +        /* Call context_saved() before releasing other waiters. */
>> +        if ( cnt == 1 )
>> +        {
>> +            if ( vprev != vnext )
>> +                context_saved(vprev);
>> +            atomic_set(&next->rendezvous_out_cnt, 0);
>> +        }
>> +        else
>> +            while ( atomic_read(&next->rendezvous_out_cnt) )
>> +                cpu_relax();
> 
> How come context_saved() is not called on this "else" branch? How
> will vprev->is_running get cleared there? Or, since everything
> else in the function is per-unit, does this clearing want to move
> here?

That's a bug I've already corrected in my version 3 (and the one which
is being tested by Sergey).

> 
>> -void context_saved(struct vcpu *prev)
>> +static void sched_slave(void)
>>   {
>> -    /* Clear running flag /after/ writing context to memory. */
>> -    smp_wmb();
>> +    struct vcpu          *vprev = current;
>> +    struct sched_unit    *prev = vprev->sched_unit, *next;
>> +    s_time_t              now;
>> +    spinlock_t           *lock;
>> +    int cpu = smp_processor_id();
> 
> unsigned int?

Yes.

> 
>> @@ -1971,6 +2164,7 @@ void __init scheduler_init(void)
>>       int i;
>>   
>>       open_softirq(SCHEDULE_SOFTIRQ, schedule);
>> +    open_softirq(SCHED_SLAVE_SOFTIRQ, sched_slave);
> 
> Noticing the "we have a race" comment and code in schedule() I
> wonder if there isn't enough state for schedule() to know
> whether to call sched_slave(), rather than having this extra
> softirq.

Especially patch 35 adds further using of SCHED_SLAVE_SOFTIRQ. I have
tried to avoid it, but the results were looking rather ugly and still
full of deadlocks.


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
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 [this message]
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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