Re: Virtio-net - add timeouts to control commands

From: Hannes Reinecke <hare@suse.de>
To: Alvaro Karsz <alvaro.karsz@solid-run.com>,
	Jason Wang <jasowang@redhat.com>
Cc: virtualization <virtualization@lists.linux-foundation.org>,
	"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: Virtio-net - add timeouts to control commands
Date: Wed, 24 Aug 2022 11:24:53 +0200	[thread overview]
Message-ID: <bedae890-80e6-9777-caff-98749d46ba3b@suse.de> (raw)
In-Reply-To: <CAJs=3_Cnf29Om2yB=JkdASuu=YBPRmZ4i7ncFfTzrftTkYZVmQ@mail.gmail.com>

On 8/24/22 11:16, Alvaro Karsz wrote:
> Hi Jason,
> 
>> Or reset but can we simply use interrupt instead of the busy waiting?
> 
> I agree that timeouts are not needed using interrupts.

Quite the contrary.
There is no guarantee that a completion for a given command will be 
signaled at all; if the completion is never posted to the virtio queue 
the VM will spin forever.

> This can be done, but seems like a big change.
> All functions calling virtnet_send_command expect to get a response immediately.
> This may be difficult, since some of the commands are sent in the
> probe function.

This is a simplistic approach. _Any_ command sent via virtio will have 
to have some sort of handling in the host, so an immediate response is 
not guaranteed.
Especially virtio-block command will _not_ be handled immediately.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
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