From: David Miller <davem@davemloft.net>
To: gregkh@linuxfoundation.org
Cc: virtio-dev@lists.oasis-open.org, anatol.pomozov@gmail.com,
mst@redhat.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org, qinchuanyu@huawei.com,
joern@logfs.org
Subject: Re: [PATCH net 1/3] kref: add kref_sub_return
Date: Wed, 12 Feb 2014 19:06:37 -0500 (EST) [thread overview]
Message-ID: <20140212.190637.328045386111912135.davem@davemloft.net> (raw)
In-Reply-To: <20140212165630.GA22991@kroah.com>
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Wed, 12 Feb 2014 08:56:30 -0800
> On Wed, Feb 12, 2014 at 06:38:21PM +0200, Michael S. Tsirkin wrote:
>> It is sometimes useful to get the value of the reference count after
>> decrement.
>> For example, vhost wants to execute some periodic cleanup operations
>> once number of references drops below a specific value, before it
>> reaches zero (for efficiency).
>
> You should never care about what the value of the kref is, if you are
> using it correctly :)
It isn't being used to determine when to destroy things.
They use it to as a heuristic of when to trigger polling.
Each ubuf attached gets a kref to the higher level virtio_net buffer
holding object, they want to trigger polling when that reference drops
to 1 or lower.
Right now they are reading the atomic refcount directly, which
I think is much worse than this helper.
next prev parent reply other threads:[~2014-02-13 0:06 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-12 16:37 [PATCH net 0/3] vhost fixes for 3.14, -stable Michael S. Tsirkin
2014-02-12 16:36 ` [PATCH net 3/3] vhost: fix a theoretical race in device cleanup Michael S. Tsirkin
2014-02-12 16:38 ` [PATCH net 2/3] vhost: fix ref cnt checking deadlock Michael S. Tsirkin
2014-02-12 16:38 ` [PATCH net 1/3] kref: add kref_sub_return Michael S. Tsirkin
2014-02-12 16:56 ` Greg Kroah-Hartman
2014-02-12 17:35 ` Michael S. Tsirkin
[not found] ` <20140212173524.GA26860@redhat.com>
2014-02-12 18:37 ` Greg Kroah-Hartman
2014-02-12 18:39 ` Anatol Pomozov
2014-02-13 0:06 ` David Miller [this message]
2014-02-13 1:25 ` Jörn Engel
2014-02-13 1:39 ` Greg KH
2014-02-13 4:05 ` David Miller
2014-02-13 4:09 ` David Miller
2014-02-14 0:03 ` Greg KH
2014-02-14 5:10 ` David Miller
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