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Re: [Qemu-devel] [PATCH v3] Throttle-down guest when live migration does

From: Chegu Vinod
Subject: Re: [Qemu-devel] [PATCH v3] Throttle-down guest when live migration does not converge.
Date: Wed, 01 May 2013 05:50:37 -0700
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130328 Thunderbird/17.0.5

On 5/1/2013 5:38 AM, Eric Blake wrote:
On 05/01/2013 06:22 AM, Chegu Vinod wrote:
Busy enterprise workloads hosted on large sized VM's tend to dirty
memory faster than the transfer rate achieved via live guest migration.
Despite some good recent improvements (& using dedicated 10Gig NICs
between hosts) the live migration does NOT converge.

Changes from v2:
- incorporated feedback from Orit, Juan and Eric
- stop the throttling thread at the start of stage 3
- rebased to latest qemu.git

+++ b/qapi-schema.json
@@ -600,9 +600,14 @@
  #          loads, by sending compressed difference of the pages
  # Since: 1.2
+# @auto-converge: Migration supports automatic throttling down of guest
+#          to force convergence. Disabled by default.
+# Since: 1.6
I've already argued that ALL new migration capabilities should be
disabled by default (see the thread on 'x-rdma-pin-all', which will be a
merge conflict if it gets applied before your patch).  So I don't think
that last sentence adds anything, and can be dropped.

I think this works, although it's the first instance of having two
top-level Since: tags on a single JSON entity.  I was envisioning:

@xbzrle: yadda... pages

@auto-convert: Migration supports... convergence (since 1.6)

Since: 1.2

to match the conventions elsewhere that the overall JSON entity (the
enum MigrationCapability) exists since 1.2, but the addition of
auto-convert happened in 1.6.

However, as nothing parses the .json file to turn it into formal docs
(yet), I'm not going to insist on a respin if this is the only problem
with your patch.  I'm not comfortable enough with my skills in reviewing
the rest of the patch, or I'd offer a reviewed-by.

I shall make the suggested changes.
Appreciate your review feedback on this part of the change.


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