On 03/31/2016 05:43 PM, Dr. David Alan Gilbert wrote:
* Li Zhijian (lizhij...@cn.fujitsu.com) wrote:
On 03/30/2016 08:05 PM, Dr. David Alan Gilbert wrote:
* Zhang Chen (zhangchen.f...@cn.fujitsu.com) 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
anything
on the socket, the result is you end up running until the end of the long
COLO
checkpoint without triggering a discompare - in my world I added a
timeout (400ms)
for an unmatched packet from the primary, where if no matching packet was
received
a checkpoint would be triggered.
5) I see the packet comparison is still the simple memcmpy that you had in
December;
are you planning on doing anything more complicated; you must be seing
most packets
miscompare?
You can see my current world at;
https://github.com/orbitfp7/qemu/commits/orbit-wp4-colo-mar16
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.
Thank you very much for your comments.
I just see you tree, you put in a lot of work(tcp comparison enhance,
sequence/acknowledge
number re-write, timeout...)
Actually, this compare module is just in a RFC stage(only including compare
frame), there are
many works to be done:
1) Integrate to COLO frame(and Let COLO primary and secondary at running state)
Yes; although I think you've had most of the code for that, also feel free to
use
any of the bits I've changed.
Thank you, we will add this part to next version.
2) ip segment defrag
Yes, this seems the hardest bit to me. It is needed for some workloads; for
example
a simple case if just an ssh connection, the differences in timing between the
primary
and secondary you see that the primary might send two short packets and the
secondary
might send one long packet with the same data.
OK, let it as a TODO issue
3) comparison base on the sequence number(tcp and udp) if packet has
Because tcp re-transmission is quit common. IRC, your code will compare the
whole tcp
packet(sequence number will be compare)
Yes; once the secondary reworks the sequence number I found the seuence number
matched most of the time on the primary.
well, let (3) (4) (5) as a TODO issue too or move it to an extra
patchset(depending on 3)
One problem (depending on the traffic)
is that the ack number might not match and I'm not sure of the best fix, for
example,
consider:
a) Send packet 1
b) Send packet 2
c) Receive response
The order of b & c is random - if the response on the same socket arrives
(c) before (b)
then the ack number in packet 2 is different; on one workload this caused a lot
of miscompares
but only if the timing is just wrong.
Yes, I've had this problem too.
the logic is a bit complicated, as kernel colo-proxy, we compare the tcp
playload(excluding sequence/ack number)
only. And introduce the 'max_ack'(max_ack = MAX(primary_max_ack,
secondary_max_ack)) to guarantee
the packet which ack is <= 'max_ack' can be release to client.
(I also had to turn off TCP timestamping to get useful comparisons)
Yes, it works.
4) packet belongs to the same connection is sort by sequence number
5) Out-Of-Oder packet handle
I think 4 & 5 both happen as part of the defrag; out of order packets were a
problem for
me on some of the workloads; I had to turn off multiqueue in one case.
6) cleanup the un-active conn_list which maybe closed. the simple way is to
introduce a
timer to record whether a connection have packet come within a timeout,
connection gone
beyond this timeout should be cleanup.
At the moment that isn't a big problem because when you receive the next
checkpoint you
can flush the list.
The only case where you have to deal with this is for continuous failover when
the
original secondary is promoted to primary, then it's connection list has to live
on longer for any connections it created prior to the failover.
Perhaps this gets more complex with defrag?
Yes, that need comparison support save/restore operation. move to TODO list.
7) Dave point out above (4)
It make sense, we will consider add this one.
8) something I miss...
For Various reasons, not all the works can be done immediately, So we hope to
discuss and
decide which function have the high priority.
Any comments and suggestions are welcome.
Yes, there's a lot of work; as I say, feel free to use any of my patches
from the world above, I wasn't planning on doing much more work on that set.
IMO, a compare frame and a COLO frame hack patch could be simple enough.
I think you'd have to show that you got some useful comparison matches;
if it almost always failed the comparison then I can't see the point.
In a word, we will enhance the comparison and try to add (1) and (7) in next
version.
PS, we will pick code from you tree. ^_^
Thanks
Li Zhijian
Dave
Thanks
Li
Dave
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 / dgilb...@redhat.com / Manchester, UK
.
--
Best regards.
Li Zhijian (8555)
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
.
