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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>,
	Julien Grall <julien.grall@arm.com>
Subject: Re: [Xen-devel] [PATCH 1/4] x86/IRQ: don't keep EOI timer running without need
Date: Thu, 6 Jun 2019 10:30:14 +0100	[thread overview]
Message-ID: <e89697d5-39c6-a059-1059-4477795f8a82@citrix.com> (raw)
In-Reply-To: <5CF8C9EE0200007800235C76@prv1-mh.provo.novell.com>

On 06/06/2019 09:08, Jan Beulich wrote:
>>>> On 05.06.19 at 19:04, <andrew.cooper3@citrix.com> 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@citrix.com>

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  reply	other threads:[~2019-06-06  9:30 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08 12:39 [PATCH 0/4] x86: EOI timer corrections / improvements Jan Beulich
2019-05-08 12:39 ` [Xen-devel] " Jan Beulich
2019-05-08 12:46 ` [PATCH 1/4] x86/IRQ: don't keep EOI timer running without need Jan Beulich
2019-05-08 12:46   ` [Xen-devel] " Jan Beulich
2019-05-16 10:32   ` Roger Pau Monné
2019-05-16 10:32     ` [Xen-devel] " Roger Pau Monné
2019-05-16 10:50     ` Jan Beulich
2019-05-16 10:50       ` [Xen-devel] " Jan Beulich
2019-05-16 11:03       ` Roger Pau Monné
2019-05-16 11:03         ` [Xen-devel] " Roger Pau Monné
2019-06-05 17:04   ` Andrew Cooper
2019-06-06  8:08     ` Jan Beulich
2019-06-06  9:30       ` Andrew Cooper [this message]
2019-05-08 12:46 ` [PATCH 2/4] x86/IRQ: bail early from irq_guest_eoi_timer_fn() when nothing is in flight Jan Beulich
2019-05-08 12:46   ` [Xen-devel] " Jan Beulich
2019-05-16 11:37   ` Roger Pau Monné
2019-05-16 11:37     ` [Xen-devel] " Roger Pau Monné
2019-05-16 12:02     ` Jan Beulich
2019-05-16 12:02       ` [Xen-devel] " Jan Beulich
2019-05-16 13:44       ` Roger Pau Monné
2019-05-16 13:44         ` [Xen-devel] " Roger Pau Monné
2019-06-05 17:15   ` Andrew Cooper
2019-06-06  8:17     ` Jan Beulich
2019-06-06 11:34       ` Andrew Cooper
2019-06-06 11:43         ` Jan Beulich
2019-06-06 11:45           ` Andrew Cooper
2019-05-08 12:47 ` [PATCH 3/4] x86/IRQ: relax locking in irq_guest_eoi_timer_fn() Jan Beulich
2019-05-08 12:47   ` [Xen-devel] " Jan Beulich
2019-05-16 13:48   ` Roger Pau Monné
2019-05-16 13:48     ` [Xen-devel] " Roger Pau Monné
2019-06-05 17:16   ` Andrew Cooper
2019-05-08 12:48 ` [PATCH 4/4] x86/IRQ: ACKTYPE_NONE cannot make it into irq_guest_eoi_timer_fn() Jan Beulich
2019-05-08 12:48   ` [Xen-devel] " Jan Beulich
2019-05-16 13:52   ` Roger Pau Monné
2019-05-16 13:52     ` [Xen-devel] " Roger Pau Monné
2019-05-16 14:48     ` Jan Beulich
2019-05-16 14:48       ` [Xen-devel] " Jan Beulich
2019-05-17  7:04     ` Jan Beulich
2019-05-17  7:04       ` [Xen-devel] " Jan Beulich
2019-06-05 17:18   ` Andrew Cooper

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