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Re: [PATCH v2 3/3] virtio-blk: Use ioeventfd_attach in start_ioeventfd


From: Hanna Czenczek
Subject: Re: [PATCH v2 3/3] virtio-blk: Use ioeventfd_attach in start_ioeventfd
Date: Fri, 9 Feb 2024 18:11:43 +0100
User-agent: Mozilla Thunderbird

On 09.02.24 15:38, Michael Tokarev wrote:
02.02.2024 18:31, Hanna Czenczek :
Commit d3f6f294aeadd5f88caf0155e4360808c95b3146 ("virtio-blk: always set
ioeventfd during startup") has made virtio_blk_start_ioeventfd() always
kick the virtqueue (set the ioeventfd), regardless of whether the BB is
drained.  That is no longer necessary, because attaching the host
notifier will now set the ioeventfd, too; this happens either
immediately right here in virtio_blk_start_ioeventfd(), or later when
the drain ends, in virtio_blk_ioeventfd_attach().

With event_notifier_set() removed, the code becomes the same as the one
in virtio_blk_ioeventfd_attach(), so we can reuse that function.

The mentioned comit is v8.2.0-812-gd3f6f294ae, - ie, past 8.2.
Is this new change still relevant for stable?

Sorry again. :/  This patch is a clean-up patch that won’t apply to 8.2.  Now, 8.2 does have basically the same logic as described in the patch message (d3f6f294aea restored it after it was broken), so a similar patch could be made for it (removing the event_notifier_set() from virtio_blk_data_plane_start()), but whether we kick the virtqueues once or twice on start-up probably won’t make a difference, certainly not in terms of correctness.

Hanna




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