linux-kernel - Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf operations

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Date:   Fri, 23 Jun 2017 10:31:28 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Zhi Wang <zhi.a.wang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     "Wang, Zhenyu Z" <zhenyu.z.wang@...el.com>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Chen, Xiaoguang" <xiaoguang.chen@...el.com>,
        "Zhang, Tina" <tina.zhang@...el.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Lv, Zhiyuan" <zhiyuan.lv@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>
Subject: Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf
 operations

On Fri, 2017-06-23 at 15:49 +0800, Zhi Wang wrote:
> Hi:
>      Thanks for the discussions! If the userspace application has 
> already maintained a LRU list, it looks like we don't need
> generation 
> anymore,

generation isn't required, things are working just fine without that. 
It is just a small optimization, userspace can skip the LRU lookup
altogether if the generation didn't change.

But of couse that only pays off if the kernel doesn't has to put much
effort into maintaining the generation id.  Something simple like
increasing it each time the guest writes a register which affects
plane_info.

If you think it doesn't make sense from the driver point of view we can
drop the generation.

cheers,
  Gerd