[zeromq-dev] Timing issues
Apostolis Xekoukoulotakis
xekoukou at gmail.com
Thu Jan 16 15:55:05 CET 2014
To reduce calls to the other layers and improve performance.
On Jan 16, 2014 4:53 PM, "Lindley French" <lindleyf at gmail.com> wrote:
> Maybe I'm missing something, but what purpose is there in disabling
> Nagle's algorithm, only to then re-implement the same concept one layer
> higher?
>
>
> On Thu, Jan 16, 2014 at 9:15 AM, Charles Remes <lists at chuckremes.com>wrote:
>
>> Nagle’s algo is already disabled in the codebase (you can confirm that
>> with a quick grep). I think what Bruno is referring to is that zeromq
>> batches small messages into larger ones before sending. This improves
>> throughput at the cost of latency as expected.
>>
>> Check out the “performance” section of the FAQ for an explanation:
>> http://zeromq.org/area:faq
>>
>>
>> On Jan 16, 2014, at 7:04 AM, Lindley French <lindleyf at gmail.com> wrote:
>>
>> Ah, that would explain it, yes. It would be great to have a way of
>> disabling Nagle's algorithm (TCP_NODELAY sockopt).
>>
>>
>> On Thu, Jan 16, 2014 at 4:24 AM, Bruno D. Rodrigues <
>> bruno.rodrigues at litux.org> wrote:
>>
>>> Without looking at the code I assume ØMQ is not trying to send each
>>> individual message as a TCP PDU but instead, as the name implies, queues
>>> messages so it can batch them together and get the performance.
>>>
>>> This then means the wire will be filled up when some internal buffer
>>> fills, or after a timeout, which looks like 100ms.
>>>
>>> On the other hand I can’t see any setsockopt to configure this possible
>>> timeout value.
>>>
>>> Any feedback from someone else before I have time to look at the code?
>>>
>>> On Jan 15, 2014, at 16:20, Lindley French <lindleyf at gmail.com> wrote:
>>>
>>> > I have a test case in which I'm communicating between two threads
>>> using zmq sockets. The fact that the sockets are in the same process is an
>>> artifact of the test, not the real use-case, so I have a TCP connection
>>> between them.
>>> >
>>> > What I'm observing is that a lot of the time, it takes ~100
>>> milliseconds between delivery of a message to the sending socket and
>>> arrival of that message on the receiving socket. Other times (less
>>> frequently) it is a matter of microseconds. I imagine this must be due to
>>> some kernel or thread scheduling weirdness, but I can't rule out that it
>>> might be due to something in 0MQ.
>>> >
>>> > If I follow the TCP socket write with one or more UDP writes using
>>> Boost.Asio, the 100 millisecond delay invariably occurs for the ZMQ TCP
>>> message but the UDP messages arrive almost instantly (before the TCP
>>> message).
>>> >
>>> > My design requires that the TCP message arrive before *most* of the
>>> UDP messages. It's fine if some come through first----UDP is faster after
>>> all, that's why I'm using it----but this big of a delay is more than I
>>> counted on, and it's concerning. I don't know if it would apply across a
>>> real network or if it's an artifact of testing in a single process.
>>> >
>>> > Any insights?
>>> > _______________________________________________
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>>>
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