linux-kernel - Re: Can vhost translate to io

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Date:   Wed, 14 Jun 2023 01:25:09 -0500
From:   michael.christie@...cle.com
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Oleg Nesterov <oleg@...hat.com>, linux@...mhuis.info,
        nicolas.dichtel@...nd.com, axboe@...nel.dk,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        sgarzare@...hat.com, jasowang@...hat.com, stefanha@...hat.com,
        brauner@...nel.org
Subject: Re: Can vhost translate to io_uring?

On 6/14/23 1:02 AM, Eric W. Biederman wrote:
> 
> I am sad my idea for simplifying things did not work out.
> 
> 
> Let's try an even bigger idea to reduce maintenance and simplify things.
> 
> Could vhost depend on io_uring?
> 
> Could vhost just be a translation layer of existing vhost requests to
> io_uring requests?
> 
> At a quick glance it looks like io_uring already supports the
> functionality that vhost supports (which I think is networking and
> scsi).
> 
> If vhost could become a translation layer that would allow removing
> the vhost worker and PF_USER_WORKER could be removed completely,
> leaving only PF_IO_WORKER.
> 
> 
> I suggest this because a significant vhost change is needed because in

It would be nice if the vhost layer could use the io-wq code as sort of
generic worker. I can look into what that would take if Jens is ok
with that type of thing.

For vhost, I just submitted a patch to the vhost layer that allow us to
switch out the vhost worker thread when IO is running:

https://lists.linuxfoundation.org/pipermail/virtualization/2023-June/067246.html

After that patch, I just need to modify vhost_worker/vhost_task_fn so
when get_signal returns true we set the worker to NULL and do a synchronize_rcu.
Then I just need to modify vhost-scsi so it detects when the worker is NULL
and modify the flush code so it handles work that didn't get to run.



> the long term the hacks in exec and coredump are not a good idea.  Which
> means something like my failed "[PATCH v3] fork, vhost: Use CLONE_THREAD
> to fix freezer/ps regression".
> 
> If we have to go to all of the trouble of reworking things it why can't
> we just make io_uring do all of the work?
> 
> Eric