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Re: [Qemu-devel] [PATCH v7 kernel 3/5] virtio-balloon: implementation of

From: Wei Wang
Subject: Re: [Qemu-devel] [PATCH v7 kernel 3/5] virtio-balloon: implementation of VIRTIO_BALLOON_F_CHUNK_TRANSFER
Date: Fri, 10 Mar 2017 19:37:28 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131028 Thunderbird/17.0.10

On 03/09/2017 10:14 PM, Matthew Wilcox wrote:
On Fri, Mar 03, 2017 at 01:40:28PM +0800, Wei Wang wrote:
From: Liang Li <address@hidden>
1) allocating pages (6.5%)
2) sending PFNs to host (68.3%)
3) address translation (6.1%)
4) madvise (19%)

This patch optimizes step 2) by transfering pages to the host in
chunks. A chunk consists of guest physically continuous pages, and
it is offered to the host via a base PFN (i.e. the start PFN of
those physically continuous pages) and the size (i.e. the total
number of the pages). A normal chunk is formated as below:
|  Base (52 bit)               | Size (12 bit)|
For large size chunks, an extended chunk format is used:
|                 Base (64 bit)               |
|                 Size (64 bit)               |
What's the advantage to extended chunks?  IOW, why is the added complexity
of having two chunk formats worth it?  You already reduced the overhead by
a factor of 4096 with normal chunks ... how often are extended chunks used
and how much more efficient are they than having several normal chunks?

Right, chunk_ext may be rarely used, thanks. I will remove chunk_ext if there is no objection from others.


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