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Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.
- To: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 3 Feb 2016 18:39:03 +0000
- Cc: Kevin Tian <kevin.tian@xxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxx>, "zhiyuan.lv@xxxxxxxxx" <zhiyuan.lv@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Zhang Yu <yu.c.zhang@xxxxxxxxxxxxxxx>, "Keir \(Xen.org\)" <keir@xxxxxxx>
- Delivery-date: Wed, 03 Feb 2016 18:39:22 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 03/02/16 18:21, George Dunlap wrote:
> 2. It's not technically difficult to extend the number of servers
> supported to something sensible, like 4 (using 4 different write_dm
> p2m types)
While technically true, spare bits in the pagetable entries are at a
premium, and steadily decreasing as Intel are introducing new features.
We have 16 current p2m types, and a finite upper bound of 6 bits of p2m
type space, already with a push to reduce this number.
While introducing 1 new p2m type for this purpose might be an acceptable
tradeoff, a using a p2m type per ioreq server is not IMO.
As an orthogonal exercise, several of the existing p2m types are
redundant and can (or are already) expressed elsehow. There is
definitely room to reduce the current 16 types down a bit without too
much effort.
~Andrew
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