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Re: [Qemu-devel] [PATCH V2 0/3] Introduce COLO-compare

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] [PATCH V2 0/3] Introduce COLO-compare
Date: Wed, 30 Mar 2016 13:05:45 +0100
User-agent: Mutt/1.5.24 (2015-08-30)

* Zhang Chen (address@hidden) wrote:
> COLO-compare is a part of COLO project. It is used
> to compare the network package to help COLO decide
> whether to do checkpoint.

Hi Zhang Chen,
  I've put comments on the individual patches, but some more general things:

  1) Please add a coment giving the example of the command line for the primary
    and secondary use of this module - it helps make it easier to understand 
the patches.

  2) There's no tracing in here - please add some; I found when I tried to get
    COLO working I needed to use lots of tracing and debugging to understand the
    packet flow.

  3) Add comments; e.g. for each function say which thread is using it and where
     the packets are coming from; e.g. 
        called from the main thread on the primary for packets arriving over 
the socket
        from the secondary.

     There's just so many packets going in so many directions it would make it
     easier to follow.

  4) A more fundamental problem is what happens if the secondary never sends 
     on the socket, the result is you end up running until the end of the long 
     checkpoint without triggering a discompare - in my world I added a timeout 
     for an unmatched packet from the primary, where if no matching packet was 
     a checkpoint would be triggered.

  5) I see the packet comparison is still the simple memcmpy that you had in 
     are you planning on doing anything more complicated; you must be seing 
most packets

You can see my current world at; 
which has my basic TCP comparison (it's only tracking incoming connections) and 
I know it's
not complete either.  It mostly works OK, although I've got an occasional seg
(which makes me wonder if I need to add the conn_list_lock I see you added).  
I'm also
not doing any TCP reassembly which is probably needed.

> v2:
>  - add jhash.h
> v1:
>  - initial patch
> Zhang Chen (3):
>   colo-compare: introduce colo compare initlization
>   colo-compare: track connection and enqueue packet
>   colo-compare: introduce packet comparison thread
>  include/qemu/jhash.h |  59 ++++
>  net/Makefile.objs    |   1 +
>  net/colo-compare.c   | 782 
> +++++++++++++++++++++++++++++++++++++++++++++++++++
>  vl.c                 |   3 +-
>  4 files changed, 844 insertions(+), 1 deletion(-)
>  create mode 100644 include/qemu/jhash.h
>  create mode 100644 net/colo-compare.c
> -- 
> 1.9.1
Dr. David Alan Gilbert / address@hidden / Manchester, UK

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