Re: [Qemu-devel] [PATCH V2 1/3] colo-compare: introduce colo compare initlization

[Jason Wang <jasowang@redhat.com>]

On 03/31/2016 05:24 PM, Dr. David Alan Gilbert wrote:
> * Zhang Chen (zhangchen.fnst@cn.fujitsu.com) wrote:
>>
>> On 03/30/2016 05:25 PM, Dr. David Alan Gilbert wrote:
>>> * Zhang Chen (zhangchen.fnst@cn.fujitsu.com) wrote:
>>>> packet come from primary char indev will be send to
>>>> outdev - packet come from secondary char dev will be drop
>>> Please put in the description an example of how you invoke
>>> the filter on the primary and secondary.
>> OK.
>> colo-compare get packet from chardev(primary_in,secondary_in),
>> and output to other chardev(outdev), so, we can use it with the
>> help of filter-mirror and filter-redirector. like that:
> Wow, this is a bit more complicated than I expected - I was expecting just one
> socket.  So let me draw this out; see comments below.
>
>> primary:
>> -netdev
>> tap,id=hn0,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown
>> -device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
>> -chardev socket,id=mirror0,host=3.3.3.3,port=9003,server,nowait
>> -chardev socket,id=compare1,host=3.3.3.3,port=9004,server,nowait
>> -chardev socket,id=compare0,host=3.3.3.3,port=9001,server,nowait
>> -chardev socket,id=compare0-0,host=3.3.3.3,port=9001
>> -chardev socket,id=compare_out,host=3.3.3.3,port=9005,server,nowait
>> -chardev socket,id=compare_out0,host=3.3.3.3,port=9005
>> -object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
>> -object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
>> -object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
>> -object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0
>             ----> mirror0: socket:secondary:9003
>             |
>         mirror-m0     <-- e1000
>             |
>             v
>         redirector-redire1 ---> compare0 socket:primary:9001 (to compare0-0)
>                           
>             -----< compare0-0 socket:primary:9001 (to compare0)
>             |  primary_in
>             |
>         compare-comp0       -----> compare_out0 socket:primary:9005
>             |
>             |  secondary_in
>             -----< compare1   socket:secondary:9004
>
> tap <-- redirector-redire0 <--- compare_out socket:primary:9005 (from compare_out0)
>
>
>> secondary:
>> -netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down
>> script=/etc/qemu-ifdown
>> -device e1000,netdev=hn0,mac=52:a4:00:12:78:66
>> -chardev socket,id=red0,host=3.3.3.3,port=9003
>> -chardev socket,id=red1,host=3.3.3.3,port=9004
>> -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
>> -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
>             ----> red0 socket::9003
>             |
> tap <-- redirector-f1 <--
>                            e1000
>     --> redirector-f2 -->
>             |
>             ----< red1 socket::9004
>
> OK, so I think we need to find a way to fix two things:
>    a) There must be an easier way of connecting two filters within the same
>       qemu than going up to the kernel's socket code, around it's TCP stack
>       and back.  Is there a better type of chardev to use we can short circuit
>       with - it shouldn't need to leave QEMU (although I can see it's easier
>       for debugging like this).  Jason/Dan - any ideas?

Looks like there's no such type of chardev. I think we could start with
tcp socket chardev first and do necessary optimization on top. In fact,
there's also advantages, with tcp sockets, the colo-compare codes could
even be an independent program out of qemu.

For the chardev type, this also reminds me one thing. Since
mirror/redirector can only work for tcp socket, we may need inspect the
chardev types and fail if not a tcp socket like what vhost-user did.


>
>    b) We should only need one socket for the connection between primary and
>       secondary - I'm not sure how to change it to let it do that.

Looks like we can (e.g for secondary):

-device e1000,netdev=hn0,mac=52:a4:00:12:78:66
-chardev socket,id=red0,host=3.3.3.3,port=9003
-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red0

If not, probably a bug.

>    c) You need to be able to turn off nagling (socket no delay) on the sockets;
>      I found a noticeable benefit of doing this on the connection between primary
>      and secondary in my world.

Right.

>
> Dave
>