From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Dario Faggioli <dario.faggioli@citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
xen-devel@lists.xenproject.org
Cc: Anshul Makkar <anshul.makkar@citrix.com>,
Meng Xu <mengxu@cis.upenn.edu>, Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH 2/3] xen: Have schedulers revise initial placement
Date: Mon, 18 Jul 2016 22:36:06 +0100 [thread overview]
Message-ID: <f3e5c646-aab0-483c-c54f-2c16ad1654d8@citrix.com> (raw)
In-Reply-To: <1468868106.13039.170.camel@citrix.com>
On 18/07/2016 19:55, Dario Faggioli wrote:
> On Mon, 2016-07-18 at 19:10 +0100, Andrew Cooper wrote:
>> On 16/07/16 15:12, Dario Faggioli wrote:
>>> On Fri, 2016-07-15 at 19:07 +0100, Andrew Cooper wrote:
>>> So you have to always keep IRQ enabled, for all scheduling
>>> operations,
>>> which is ok for _almost_ all of them, with the only exception of
>>> the
>>> wakeup of a vcpu.
>> I know that it is all or nothing. What specific action about waking
>> a
>> vcpu requires holding a lock?
>>
>> If it is simply re-queueing the vcpu onto the runable queue, there
>> are a
>> number of lockless queuing algorithms which can be used.
>>
> Yes, it's vcpu_wake() that does vcpu_schedule_lock_irqsave() before,
> among other things, calling SCHED_OP(wake, v).
Right - this looks easy to fix. Use a per-pcpu single linked list,
which can be mutated safely with cmpxchg() rather than locks, have
vcpu_wake() add v to the linked list, and schedule itself a
SCHEDULE_SOFTIRQ, (possibly a new SCHEDULE_WAKE_SOFTIRQ with higher
priority than SCHEDULE_SOFTIRQ).
Then in the schedule softirq can take the vcpu schedule lock without
disabling interrupts and run the internals of what is currently
vcpu_wake(). The current content of vcpu_wake() very large for what is
typically executed from interrupt context.
~Andrew
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next prev parent reply other threads:[~2016-07-18 21:36 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-15 18:02 [PATCH 1/3] xen: Some code motion to avoid having to do forward-declaration George Dunlap
2016-07-15 18:02 ` [PATCH 2/3] xen: Have schedulers revise initial placement George Dunlap
2016-07-15 18:07 ` Andrew Cooper
2016-07-16 14:12 ` Dario Faggioli
2016-07-18 18:10 ` Andrew Cooper
2016-07-18 18:55 ` Dario Faggioli
2016-07-18 21:36 ` Andrew Cooper [this message]
2016-07-19 7:14 ` Dario Faggioli
2016-07-18 10:28 ` Dario Faggioli
2016-07-25 11:17 ` George Dunlap
2016-07-25 14:36 ` Meng Xu
2016-07-26 9:17 ` Dario Faggioli
2016-07-25 14:35 ` Meng Xu
2016-08-01 10:40 ` Jan Beulich
2016-08-01 12:32 ` Dario Faggioli
2016-08-05 13:24 ` Jan Beulich
2016-08-05 14:09 ` Dario Faggioli
2016-08-05 14:44 ` Jan Beulich
2016-08-11 14:59 ` Dario Faggioli
2016-08-11 15:51 ` Andrew Cooper
2016-08-11 23:35 ` Dario Faggioli
2016-08-12 1:59 ` dependences for backporting to 4.6 [was: Re: [PATCH 2/3] xen: Have schedulers revise initial placement] Dario Faggioli
2016-08-12 13:53 ` Jan Beulich
2016-08-16 10:21 ` Dario Faggioli
2016-08-16 11:21 ` Jan Beulich
2016-08-12 8:58 ` dependences for backporting to 4.5 " Dario Faggioli
2016-07-15 18:02 ` [PATCH 3/3] xen: Remove buggy initial placement algorithm George Dunlap
2016-07-15 18:10 ` Andrew Cooper
2016-07-16 13:55 ` Dario Faggioli
2016-07-18 10:03 ` George Dunlap
2016-07-16 15:48 ` [PATCH 1/3] xen: Some code motion to avoid having to do forward-declaration Meng Xu
2016-07-18 9:58 ` Dario Faggioli
2016-07-18 10:06 ` George Dunlap
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