Re: [PATCH 1/6] xen/sched: call cpu_disable_scheduler() via cpu notifier

From: Juergen Gross <jgross@suse.com>
To: Dario Faggioli <dfaggioli@suse.com>, xen-devel@lists.xenproject.org
Cc: "George Dunlap" <george.dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wei.liu2@citrix.com>,
	"Jan Beulich" <jbeulich@suse.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH 1/6] xen/sched: call cpu_disable_scheduler() via cpu notifier
Date: Wed, 27 Mar 2019 17:53:46 +0100	[thread overview]
Message-ID: <6b1cfffb-02ae-4859-94aa-29676b0c18da@suse.com> (raw)
In-Reply-To: <4585c758d5e6928acf5ed714ad5f13bf3991492f.camel@suse.com>

On 27/03/2019 17:51, Dario Faggioli wrote:
> On Wed, 2019-03-27 at 17:31 +0100, Juergen Gross wrote:
>> On 27/03/2019 17:24, Dario Faggioli wrote:
>>> On Mon, 2019-03-18 at 14:11 +0100, Juergen Gross wrote:
>>>> cpu_disable_scheduler() is being called from __cpu_disable()
>>>> today.
>>>> There is no need to call it on the cpu just being disabled, so
>>>> use
>>>> the CPU_DEAD case of the cpu notifier chain.
>>>>
>>> So, what do you mean with "There is no need to call it on the cpu
>>> just
>>> being disabled"?
>>>
>>> Because we still (even after this patch, I mean) call
>>> cpu_disable_scheduler() on all non-boot CPUs, aren't we? It's just
>>> that
>>> right now we call it from __cpu_disable(), with the patch we call
>>> it
>>> slightly later.
>>
>> The CPU_DEAD notifier chain is called on the CPU requesting the other
>> one to go down (so on the boot CPU in suspend case). So we call it
>> _for_
>> all non-boot CPUs in the boot CPU.
>>
> Mmm... ok, I see what you mean now.
> 
> I guess part of "the problem" is that "call func on cpu A" reads, at
> least to me, as both 1) call func so that it acts on and change the
> state of cpu A, and 2) call func in such a way that it executes on cpu
> A.

I'll rephrase to "execute func on cpu...".

Juergen

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