Re: [Xen-devel] Remus' Network Buffering

[Shriram Rajagopalan <rshriram@xxxxxxxxx>]

On Thu, Apr 19, 2012 at 9:15 AM, Rahul Singh <singh.rahul.1983@xxxxxxxxx> wrote:

Hi,
I am trying to understand and change the network buffering that is being used by Remus, the HA solution present in Xen. From what i understood from reading the code, Remus calls the postsuspend method of the BufferedNIC after it suspends the domain that sends TC_PLUG_CHECKPOINT message and start the buffering

for packets in the "next" epoch [the one that starts after the domain is resumed]
 

and then calls the commit method of BufferedNIC after it gets the acknowledgement that sends the TC_PLUG_RELEASE message and releases the buffered packets.

of the previous current epoch [the one whose checkpoint was just committed on the backup machine]
 

I have the following doubts
1) How does remus ensure that the packets gets buffered for an entire epoch ?

I would suggest you go through the comments in
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=net/sched/sch_plug.c;h=89f8fcf73f18f6e091881cc829861285c0c8f8b7;hb=HEAD
the sch_plug module in upstream linux.

2) If i comment out the lines in the "postsuspend" and "commit" lines of the BufferedNIC class that send the TC_PLUG_CHECKPOINT and TC_PLUG_RELEASE, i see that all the network packets are being buffered and i cannot ping the Remus-protected VM at all. Where is the packet buffering happen if i comment out these 2 lines ?

the module starts out in the buffered mode and releases packets only upon receiving a RELEASE command.

hope that helps.

cheers
shriram
 

Thanking you,
Rahul.

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