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Re: [Xen-devel] [PATCH 1/4] x86/IRQ: don't keep EOI timer running without need
- To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 6 Jun 2019 10:30:14 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>
- Delivery-date: Thu, 06 Jun 2019 09:30:37 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 06/06/2019 09:08, Jan Beulich wrote:
>>>> On 05.06.19 at 19:04, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 08/05/2019 13:46, Jan Beulich wrote:
>>> The timer needs to remain active only until all pending IRQ instances
>>> have seen EOIs from their respective domains. Stop it when the in-flight
>>> count has reached zero in desc_guest_eoi(). Note that this is race free
>>> (with __do_IRQ_guest()), as the IRQ descriptor lock is being held at
>>> that point.
>>>
>>> Also pull up stopping of the timer in __do_IRQ_guest() itself: Instead
>>> of stopping it immediately before re-setting, stop it as soon as we've
>>> made it past any early returns from the function (and hence we're sure
>>> it'll get set again).
>> Why this this a good thing?
> For it to not fire when it doesn't need to. If we're about to set
> a new timeout, we clearly don't want the previous one to have
> any effect anymore.
Sounds like an excellent addition to the code, now that there is a
order-of-returns dependency.
With a suitable comment, Reviewed-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>
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