linux-kernel - Re: [RFC] virtio_scsi: to poll and kick the virtqueue in timeout handler

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Message-ID: <ac161748-15d2-2962-402e-23abca469623@suse.de>
Date:   Sun, 23 May 2021 09:39:51 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        virtualization@...ts.linux-foundation.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     mst@...hat.com, jasowang@...hat.com, pbonzini@...hat.com,
        stefanha@...hat.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, joe.jin@...cle.com,
        junxiao.bi@...cle.com, srinivas.eeda@...cle.com
Subject: Re: [RFC] virtio_scsi: to poll and kick the virtqueue in timeout
 handler

On 5/23/21 8:38 AM, Dongli Zhang wrote:
> This RFC is to trigger the discussion about to poll and kick the
> virtqueue on purpose in virtio-scsi timeout handler.
> 
> The virtio-scsi relies on the virtio vring shared between VM and host.
> The VM side produces requests to vring and kicks the virtqueue, while the
> host side produces responses to vring and interrupts the VM side.
> 
> By default the virtio-scsi handler depends on the host timeout handler
> by BLK_EH_RESET_TIMER to give host a chance to perform EH.
> 
> However, this is not helpful for the case that the responses are available
> on vring but the notification from host to VM is lost.
> 
How can this happen?
If responses are lost the communication between VM and host is broken, 
and we should rather reset the virtio rings themselves.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
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