[ovs-dev] [PATCH] python: Allow specifying the iterations in Idl.run

[Jason Kölker]

On Wed, Mar 23, 2016 at 6:29 PM, Ben Pfaff <blp at ovn.org> wrote:
> On Sun, Mar 20, 2016 at 03:29:06AM +0000, Jason Kölker wrote:
>> Callers to Idl.run() should be able to specify the number of iterations
>> to run in one call. Instrumentation revealed that a call to Idl.run() with a
>> can block up to a few seconds, with most of the time being spent parsing
>> messages.
>>
>> Since parsing is a CPU only task eventlet and friends are unable to
>> to provide concurrency. Specifying a configurable number of iterations
>> will allow calling code to better manage concurrency.
>>
>> Signed-off-by: Jason Kölker <jason at koelker.net>
>
> A couple of seconds is really extreme.  I'm actually shocked to hear
> that parsing 4 kB * 200 == 800 kB of data can take multiple seconds.

I'm still working on tracking it all down. I *think* it has something to do
with the socket stream buffering. But as we only see it from time to time
on our controller and running just the Idl under eventlet (no other services)
doesn't have the same behavior; its been slow getting a reproducible case.

>  If it takes that long, then I'd suggest an approach different from this
> patch.  First, reduce the iteration count from 50 to something smaller.
> Second, figure out why JSON parsing is so slow, and fix it.

Agreed. This was next on my list to start going through the JSON parser and
instrumenting it to track it down, once I can get a good test to
reproduce reliably.

> stackoverflow points to some JSON push parsers:
> http://stackoverflow.com/questions/444380/is-there-a-streaming-api-for-json

Thanks! I'll look through the them and compare and see if there are some speed
ups we can use. I briefly looked at what it would take to replace the
parser with
ijson. That might be the direction I try to go long term, but I'd
rather not have an
external dependency. I'll carry this patch internally for the time
being until I can
better understand whats really going on.

Happy Hacking!

7-11