[concurrency-interest] Blocking vs. non-blocking

Zhong Yu zhong.j.yu at gmail.com
Tue Aug 5 13:10:33 EDT 2014


On Tue, Aug 5, 2014 at 9:40 AM, David M. Lloyd <david.lloyd at redhat.com> wrote:
> I don't have updated benchmarks, but we researched this extensively and
> found that for server applications, and with clean, optimized
> implementations, non-blocking I/O has a large advantave, especially with
> 1,000s+ connections

I forgot to emphasize that my test was for a single, half-duplex
connection, designed to compare how much self-time each server impl
spends on a request-response cycle.

> and even with blocking workers (i.e. servlets). Tomcat
> is (please forgive me for saying it) not really a good example of *anything*
> beyond "how people used to code back in 1999".
>
> Take this with a BIG grain of salt, but this might give you an idea as to
> the relative performance status quo of various approaches and languages in
> terms of I/O:
>
> http://www.techempower.com/benchmarks/
>
> Relying on papers from a decade ago, and software from even longer ago, is
> probably even less useful than one might expect.  CPU architectures,
> kernels, Java itself, and the knowledge and experience of those writing Java
> software, have come a very, very long way since then.
>
>
> On 08/05/2014 09:12 AM, Oleksandr Otenko wrote:
>>
>> That still leaves everyone wonder why one would prefer to code in
>> continuation-passing style compared to straightforward blocking IO. Both
>> IO being on par is not reason enough to switch.
>>
>> Alex
>>
>> On 03/08/2014 20:06, Zhong Yu wrote:
>>>>
>>>> Also, apparently, in heavy I/O scenarios, you may have a much better
>>>> system
>>>> throughput waiting for things to happen in I/O (blocking I/O) vs being
>>>> notified of I/O events (Selector-based I/O):
>>>> http://www.mailinator.com/tymaPaulMultithreaded.pdf. Paper is 6 years
>>>> old
>>>> and kernel/Java realities might have changed, YMMV, but the difference
>>>> is(was?) impressive. Also, Apache HTTP Client still swears by
>>>> blocking I/O
>>>> vs non-blocking one in terms of efficiency:
>>>> http://wiki.apache.org/HttpComponents/HttpClient3vsHttpClient4vsHttpCore
>>>
>>> To add a small data point to this discussion, Tomcat with NIO is
>>> apparently slower than Tomcat with Blocking-IO by 1,700ns for a simple
>>> request-response, according to a benchmark I did recently [1]. But!
>>> The difference is very small, and I would argue that it is negligible.
>>>
>>> Paul Tyma's claim (that the throughput of Blocking-IO is 30% more than
>>> NIO) is not very meaningful for real applications. I did once
>>> replicate his claim with a test that does nothing with the bytes being
>>> transferred; but as soon as you at least read each byte once, the
>>> throughput difference becomes very unimpressive (and frankly I suspect
>>> it's largely due to Java's implementation of NIO).
>>>
>>> [1] http://bayou.io/draft/Comparing_Java_HTTP_Servers_Latencies.html
>>>
>>> Zhong Yu
>>> bayou.io
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>>> Concurrency-interest at cs.oswego.edu
>>> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
>>
>>
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>
> --
> - DML
>
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