From: Jason Gunthorpe <jgg@ziepe.ca>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Grzegorz Jaszczyk <jaz@semihalf.com>,
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Subject: Re: [PATCH 0/2] eventfd: simplify signal helpers
Date: Tue, 18 Jul 2023 12:56:38 -0300 [thread overview]
Message-ID: <ZLa2NmwexoxPkS9a@ziepe.ca> (raw)
In-Reply-To: <20230717165203.4ee6b1e6.alex.williamson@redhat.com>
On Mon, Jul 17, 2023 at 04:52:03PM -0600, Alex Williamson wrote:
> On Mon, 17 Jul 2023 19:12:16 -0300
> Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> > On Mon, Jul 17, 2023 at 01:08:31PM -0600, Alex Williamson wrote:
> >
> > > What would that mechanism be? We've been iterating on getting the
> > > serialization and buffering correct, but I don't know of another means
> > > that combines the notification with a value, so we'd likely end up with
> > > an eventfd only for notification and a separate ring buffer for
> > > notification values.
> >
> > All FDs do this. You just have to make a FD with custom
> > file_operations that does what this wants. The uAPI shouldn't be able
> > to tell if the FD is backing it with an eventfd or otherwise. Have the
> > kernel return the FD instead of accepting it. Follow the basic design
> > of eg mlx5vf_save_fops
>
> Sure, userspace could poll on any fd and read a value from it, but at
> that point we're essentially duplicating a lot of what eventfd provides
> for a minor(?) semantic difference over how the counter value is
> interpreted. Using an actual eventfd allows the ACPI notification to
> work as just another interrupt index within the existing vfio IRQ
> uAPI.
Yes, duplicated, sort of, whatever the "ack" is to allow pushing a new
value can be revised to run as part of the read.
But I don't really view it as a minor difference. eventfd is a
counter. It should not be abused otherwise, even if it can be made to
work.
It really isn't an IRQ if it is pushing an async message w/data.
Jason
next prev parent reply other threads:[~2023-07-18 15:58 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230630155936.3015595-1-jaz@semihalf.com>
2023-07-14 7:05 ` [PATCH 0/2] eventfd: simplify signal helpers Christian Brauner
2023-07-14 15:24 ` Jason Gunthorpe
2023-07-17 8:29 ` Grzegorz Jaszczyk
2023-07-17 19:08 ` Alex Williamson
2023-07-17 22:12 ` Jason Gunthorpe
2023-07-17 22:52 ` Alex Williamson
2023-07-18 15:56 ` Jason Gunthorpe [this message]
2023-07-13 10:05 Christian Brauner
2023-07-13 17:10 ` Alex Williamson
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