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From: John Garry <john.garry@huawei.com>
To: Christoph Hellwig <hch@lst.de>, Thomas Gleixner <tglx@linutronix.de>
Cc: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	<linux-block@vger.kernel.org>, <linux-nvme@lists.infradead.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	Bjorn Helgaas <bhelgaas@google.com>, <linux-pci@vger.kernel.org>,
	Sagi Grimberg <sagi@grimberg.me>, Daniel Wagner <dwagner@suse.de>,
	Wen Xiong <wenxiong@us.ibm.com>, Hannes Reinecke <hare@suse.de>,
	Keith Busch <kbusch@kernel.org>, Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH V4 1/3] driver core: mark device as irq affinity managed if any irq is managed
Date: Wed, 21 Jul 2021 10:44:53 +0100	[thread overview]
Message-ID: <fe34623e-1074-862d-e822-7359ae4def0f@huawei.com> (raw)
In-Reply-To: <20210721072445.GA11257@lst.de>

+ Marc

On 21/07/2021 08:24, Christoph Hellwig wrote:
> On Wed, Jul 21, 2021 at 09:20:00AM +0200, Thomas Gleixner wrote:
>>> Just walking the list seems fine to me given that this is not a
>>> performance criticial path.  But what are the locking implications?
>> At the moment there are none because the list is initialized in the
>> setup path and never modified afterwards. Though that might change
>> sooner than later to fix the virtio wreckage vs. MSI-X.
> What is the issue there?  Either way, if we keep the helper in the
> IRQ code it should be easy to spot for anyone adding the locking.
> 
>>> Also does the above imply this won't work for your platform MSI case?
>> The msi descriptors are attached to struct device and independent of
>> platform/PCI/whatever.
> That's what I assumed, but this text from John suggested there is
> something odd about the platform case:
> 
> "Did you consider that for PCI .."
> .

For this special platform MSI case there is a secondary interrupt 
controller (called mbigen) which generates the MSI on behalf of the 
device, which I think the MSI belongs to (and not the device, itself).

See "latter case" mentioned in commit 91f90daa4fb2.

I think Marc and Thomas can explain this much better than I could.

Anyway, as I mentioned earlier, I think that this specific problem is 
unique and can be solved without using a function which examines the 
struct device.msi_list .

Thanks,
John

  reply	other threads:[~2021-07-21 10:01 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 12:08 [PATCH V4 0/3] blk-mq: fix blk_mq_alloc_request_hctx Ming Lei
2021-07-15 12:08 ` [PATCH V4 1/3] driver core: mark device as irq affinity managed if any irq is managed Ming Lei
2021-07-15 12:40   ` Greg Kroah-Hartman
2021-07-16  2:17     ` Ming Lei
2021-07-16 20:01   ` Bjorn Helgaas
2021-07-17  9:30     ` Ming Lei
2021-07-21  0:30       ` Bjorn Helgaas
2021-07-19  7:51   ` John Garry
2021-07-19  9:44     ` Christoph Hellwig
2021-07-19 10:39       ` John Garry
2021-07-20  2:38         ` Ming Lei
2021-07-21  7:20       ` Thomas Gleixner
2021-07-21  7:24         ` Christoph Hellwig
2021-07-21  9:44           ` John Garry [this message]
2021-07-21 20:22             ` Thomas Gleixner
2021-07-22  7:48               ` John Garry
2021-07-21 20:14           ` Thomas Gleixner
2021-07-21 20:32             ` Christoph Hellwig
2021-07-21 22:38               ` Thomas Gleixner
2021-07-22  7:46                 ` Christoph Hellwig
2021-07-15 12:08 ` [PATCH V4 2/3] blk-mq: mark if one queue map uses managed irq Ming Lei
2021-07-15 12:08 ` [PATCH V4 3/3] blk-mq: don't deactivate hctx if managed irq isn't used Ming Lei

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