From: Juergen Gross <jgross@suse.com>
To: Dario Faggioli <dfaggioli@suse.com>,
"andrii.anisov@gmail.com" <andrii.anisov@gmail.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "sstabellini@kernel.org" <sstabellini@kernel.org>,
"andrii_anisov@epam.com" <andrii_anisov@epam.com>,
"george.dunlap@eu.citrix.com" <george.dunlap@eu.citrix.com>,
"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
"tim@xen.org" <tim@xen.org>,
"julien.grall@arm.com" <julien.grall@arm.com>,
Jan Beulich <JBeulich@suse.com>
Subject: Re: [Xen-devel] [RFC 0/6] XEN scheduling hardening
Date: Mon, 29 Jul 2019 14:13:55 +0200 [thread overview]
Message-ID: <f9ebb773-db7b-f466-2c77-302bc3e2ed51@suse.com> (raw)
In-Reply-To: <41291327c741e276b4ad666e67152b74d2257a42.camel@suse.com>
On 29.07.19 13:53, Dario Faggioli wrote:
> On Fri, 2019-07-26 at 14:14 +0200, Juergen Gross wrote:
>> On 26.07.19 13:56, Dario Faggioli wrote:
>>> On Fri, 2019-07-26 at 13:37 +0300, Andrii Anisov wrote:
>>>> - How to avoid the absolute top priority of tasklets (what is
>>>> obeyed
>>>> by all
>>>> schedulers so far). Should idle vcpu be scheduled as the
>>>> normal
>>>> guest vcpus
>>>> (through queues, priorities, etc)?
>>>>
>>> Therefore, even if there wouldn't be any subsystem explicitly
>>> relying
>>> on the current behavior (which should be verified), I think we are
>>> at
>>> high risk of breaking things, if we change.
>>
>> We'd break things IMO.
>>
>> Tasklets are sometimes used to perform async actions which can't be
>> done
>> in guest vcpu context. Like switching a domain to shadow mode for
>> L1TF
>> mitigation, or marshalling all cpus for stop_machine(). You don't
>> want
>> to be able to block tasklets, you want them to run as soon as
>> possible.
>>
> Yep, stop-machine was precisely what I had in mind, but as Juergen
> says, there's more.
>
> As said, I suggest we defer this problem or, in general, we treat it
> outside of this series.
>
>>> 2) you move all these activities out of idle, and in some other
>>> context, and you let idle just do the idling. At that point,
>>> time
>>> accounted to idle will be only actual idle time, as the time it
>>> took to Xen to do all the other things is now accounted to the
>>> new
>>> execution context which is running them.
>>
>> And here we are coming back to the idea of a "hypervisor domain" I
>> suggested about 10 years ago and which was rejected at that time...
>>
> It's pretty much what Andrii is proposing already, when he says he'd
> consider idle_vcpu an 'hypervisor vcpu'. Or at least a naturale
> extension of that.
The main difference is its priority and the possibility to allow it to
become blocked.
> I don't know what was the occasion for proposing it, and the argument
> against it, 10 years ago, so I won't comment on that. :-D
It was in the discussion of my initial submission of cpupools. It was
one alternative thought to solve the continue_hypercall_on_cpu()
problem. In the end that was done via tasklets. :-)
Juergen
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next prev parent reply other threads:[~2019-07-29 12:14 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 10:37 [Xen-devel] [RFC 0/6] XEN scheduling hardening Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 1/6] xen/arm: Re-enable interrupt later in the trap path Andrii Anisov
2019-07-26 10:48 ` Julien Grall
2019-07-30 17:35 ` Andrii Anisov
2019-07-30 20:10 ` Julien Grall
2019-08-01 6:45 ` Andrii Anisov
2019-08-01 9:37 ` Julien Grall
2019-08-02 8:28 ` Andrii Anisov
2019-08-02 9:03 ` Julien Grall
2019-08-02 12:24 ` Andrii Anisov
2019-08-02 13:22 ` Julien Grall
2019-08-01 11:19 ` Dario Faggioli
2019-08-02 7:50 ` Andrii Anisov
2019-08-02 9:15 ` Julien Grall
2019-08-02 13:07 ` Andrii Anisov
2019-08-02 13:49 ` Julien Grall
2019-08-03 1:39 ` Dario Faggioli
2019-08-03 0:55 ` Dario Faggioli
2019-08-06 13:09 ` Andrii Anisov
2019-08-08 14:07 ` Andrii Anisov
2019-08-13 14:45 ` Dario Faggioli
2019-08-15 18:25 ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 2/6] schedule: account true system idle time Andrii Anisov
2019-07-26 12:00 ` Dario Faggioli
2019-07-26 12:42 ` Andrii Anisov
2019-07-29 11:40 ` Dario Faggioli
2019-08-01 8:23 ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 3/6] sysctl: extend XEN_SYSCTL_getcpuinfo interface Andrii Anisov
2019-07-26 12:15 ` Dario Faggioli
2019-07-26 13:06 ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 4/6] xentop: show CPU load information Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 5/6] arm64: сall enter_hypervisor_head only when it is needed Andrii Anisov
2019-07-26 10:44 ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 5/6] arm64: call " Andrii Anisov
2019-07-26 10:59 ` Julien Grall
2019-07-30 17:35 ` Andrii Anisov
2019-07-31 11:02 ` Julien Grall
2019-07-31 11:33 ` Andre Przywara
2019-08-01 7:33 ` Andrii Anisov
2019-08-01 10:17 ` Julien Grall
2019-08-02 13:50 ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 6/6] schedule: account all the hypervisor time to the idle vcpu Andrii Anisov
2019-07-26 11:56 ` [Xen-devel] [RFC 0/6] XEN scheduling hardening Dario Faggioli
2019-07-26 12:14 ` Juergen Gross
2019-07-29 11:53 ` Dario Faggioli
2019-07-29 12:13 ` Juergen Gross [this message]
2019-07-29 14:47 ` Andrii Anisov
2019-07-29 18:46 ` Dario Faggioli
2019-07-29 14:28 ` Andrii Anisov
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