linux-kernel - Re: [PATCH 6/6] drivers: enable xenwatch multithreading for xen-netback and xen-blkback driver

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Message-ID: <518d3ec9-0d2d-7f77-e750-3e1329f7e97b@suse.com>
Date:   Fri, 14 Sep 2018 11:16:30 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     boris.ostrovsky@...cle.com, paul.durrant@...rix.com,
        wei.liu2@...rix.com, konrad.wilk@...cle.com, roger.pau@...rix.com,
        srinivas.eeda@...cle.com
Subject: Re: [PATCH 6/6] drivers: enable xenwatch multithreading for
 xen-netback and xen-blkback driver

On 14/09/18 09:34, Dongli Zhang wrote:
> This is the 6th patch of a (6-patch) patch set.
> 
> As the 'use_mtwatch' for xen-netback and xen-blkback are set to true,
> probing any xenbus devices of those two drivers would create the per-domU
> xenwatch thread for the domid the new devices belong to, or increment the
> reference count  of existing thread.
> 
> Xenwatch multithreading might be enabled for more xen backend pv drivers in
> the future.
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> ---
>  drivers/block/xen-blkback/xenbus.c | 3 ++-
>  drivers/net/xen-netback/xenbus.c   | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index a4bc74e..debbbd0 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -1108,7 +1108,8 @@ static struct xenbus_driver xen_blkbk_driver = {
>  	.ids  = xen_blkbk_ids,
>  	.probe = xen_blkbk_probe,
>  	.remove = xen_blkbk_remove,
> -	.otherend_changed = frontend_changed
> +	.otherend_changed = frontend_changed,
> +	.use_mtwatch = true,
>  };
>  
>  int xen_blkif_xenbus_init(void)
> diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
> index cd51492..63d46a7 100644
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -1203,6 +1203,7 @@ static struct xenbus_driver netback_driver = {
>  	.remove = netback_remove,
>  	.uevent = netback_uevent,
>  	.otherend_changed = frontend_changed,
> +	.use_mtwatch = true,

Is there a special reason why kernel based backends shouldn't all use
the multithread model? This would avoid the need for the use_mtwatch
struct member.

This is meant as an honest question. I'm really not sure we should
switch all backends at once. OTOH I can't see any real downsides.

Thoughts?


Juergen