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Re: [Qemu-devel] [RFC PATCH v2] Throttle-down guest when live migration


From: Chegu Vinod
Subject: Re: [Qemu-devel] [RFC PATCH v2] Throttle-down guest when live migration does not converge.
Date: Mon, 29 Apr 2013 10:48:08 -0700
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130328 Thunderbird/17.0.5

On 4/29/2013 7:53 AM, Eric Blake wrote:
On 04/27/2013 02:50 PM, 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.

No exernal trigger is required (unlike option 1) and it can co-exist
s/exernal/external/

with enhancements being pursued as part of Option 2 (e.g. RDMA).

Thanks to Juan and Paolo for their useful suggestions.

---

(qemu) info migrate
capabilities: xbzrle: off auto-converge: on   <----
This part looks nice.

I'm not reviewing the entire patch (I'm not an expert on the internals
of migration), but just the interface:

Thanks for taking a look at this. I shall incorporate your suggested changes in the
next version.

Hoping to hear from Juan/Orit and others on the live migration part.

Thanks,
Vinod

+++ b/qapi-schema.json
@@ -599,10 +599,14 @@
  #          This feature allows us to minimize migration traffic for certain 
work
  #          loads, by sending compressed difference of the pages
  #
+# @auto-converge: Controls whether or not the we want the migration to
+#          automaticially detect and force convergence by slowing
s/automaticially/automatically/

+#          down the guest. Disabled by default.
Missing a (since 1.6) designation.

Also, use of first-person (us, we) in docs seems a bit unprofessional,
although you were copying pre-existing usage.  How about:

@xbzrle: Migration supports xbzrle (Xor Based Zero Run Length Encoding),
          which minimizes migration traffic for certain workloads by
          sending compressed differences of active pages

@auto-converge: Migration supports automatic throttling of guest
                 activity to force convergence (since 1.6)





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