[zeromq-dev] Timing issues

[Lindley French]

Okay, fair enough. Not every use-case calls for throughput to trump
latency, though, so it would be good to make that an optional feature.


On Thu, Jan 16, 2014 at 9:57 AM, Apostolis Xekoukoulotakis <
xekoukou at gmail.com> wrote:

> http://www.aosabook.org/en/zeromq.html
> On Jan 16, 2014 4:55 PM, "Apostolis Xekoukoulotakis" <xekoukou at gmail.com>
> wrote:
>
>> 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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