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Re: [Xen-devel] [PATCH 0001/001] xen: multi page ring support for block devices
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
- Date: Wed, 7 Mar 2012 10:15:54 -0500
- Cc: "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>, "waldi@xxxxxxxxxx" <waldi@xxxxxxxxxx>, "netdev@xxxxxxxxxxxxxxx" <netdev@xxxxxxxxxxxxxxx>, "rusty@xxxxxxxxxxxxxxx" <rusty@xxxxxxxxxxxxxxx>, joe.jin@xxxxxxxxxx, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "jbarnes@xxxxxxxxxxxxxxxx" <jbarnes@xxxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxx>, "paul.gortmaker@xxxxxxxxxxxxx" <paul.gortmaker@xxxxxxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, "weiyi.huang@xxxxxxxxx" <weiyi.huang@xxxxxxxxx>, Santosh Jodh <Santosh.Jodh@xxxxxxxxxx>, "linux-pci@xxxxxxxxxxxxxxx" <linux-pci@xxxxxxxxxxxxxxx>, dgdegra@xxxxxxxxxxxxx, "virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx" <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, "lersek@xxxxxxxxxx" <lersek@xxxxxxxxxx>, "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>
- Delivery-date: Wed, 07 Mar 2012 16:11:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Mar 7, 2012 4:33 AM, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>
> >>> On 06.03.12 at 18:20, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> wrote:
> > -> the usage of XenbusStateInitWait? Why do we introduce that? Looks
> > like a fix to something.
>
> No, this is required to get the negotiation working (the frontend must
> not try to read the new nodes until it can be certain that the backend
> populated them). However, as already pointed out in an earlier reply
> to Santosh, the way this is done here doesn't appear to allow for the
> backend to already be in InitWait state when the frontend gets
> invoked.
OK.
>
> > -> XENBUS_MAX_RING_PAGES - why 2? Why not 4? What is the optimal
> > default size for SSD usage? 16?
>
> What do SSDs have to do with a XenBus definition? Imo it's wrong (and
> unnecessary) to introduce a limit at the XenBus level at all - each driver
> can do this for itself.
The patch should mention what the benefit of multi ring is.
>
> As to the limit for SSDs in the block interface - I don't think the number
> of possibly simultaneous requests has anything to do with this. Instead,
> I'd expect the request number/size/segments extension that NetBSD
> apparently implements to possibly have an effect.
.. which sounds to me like increasing the bandwidth of the protocol. Should be mentioned somewhere in the git description.
>
> Jan
>
>
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