From: Thomas Gleixner <tglx@linutronix.de>
To: Christoph Hellwig <hch@lst.de>
Cc: Christoph Hellwig <hch@lst.de>,
John Garry <john.garry@huawei.com>,
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>
Subject: Re: [PATCH V4 1/3] driver core: mark device as irq affinity managed if any irq is managed
Date: Wed, 21 Jul 2021 22:14:25 +0200 [thread overview]
Message-ID: <871r7rqva6.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210721072445.GA11257@lst.de>
On Wed, Jul 21 2021 at 09:24, 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.
https://lore.kernel.org/r/87o8bxcuxv.ffs@nanos.tec.linutronix.de
TLDR: virtio allocates ONE irq on msix_enable() and then when the guest
actually unmasks another entry (e.g. request_irq()), it tears down the
allocated one and set's up two. On the third one this repeats ....
There are only two options:
1) allocate everything upfront, which is undesired
2) append entries, which might need locking, but I'm still trying to
avoid that
There is another problem vs. vector exhaustion which can't be fixed that
way, but that's a different story.
Thanks,
tglx
next prev parent reply other threads:[~2021-07-21 20:14 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
2021-07-21 20:22 ` Thomas Gleixner
2021-07-22 7:48 ` John Garry
2021-07-21 20:14 ` Thomas Gleixner [this message]
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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