Cloud Haskell and network latency issues with -threaded

Tim Watson watson.timothy at
Wed Feb 6 15:09:22 CET 2013

Hi Kostirya,

I'm putting the parallel-haskell and ghc-users lists on cc, just in case other (better informed) folks want to chip in here.


First of all, I'm assuming you're talking about network latency when compiling with -threaded - if not I apologise for misunderstanding!

There is apparently an outstanding network latency issue when compiling with -threaded, but according to a conversation I had with the other developers on #haskell-distributed, this is not something that's specific to Cloud Haskell. It is something to do with the threaded runtime system, so would need to be solved for GHC (or is it just the Network package!?) in general. Writing up a simple C program and equivalent socket use in Haskell and comparing the latency using -threaded will show this up.

See the latency section in for some more details. According to that, there *are* some things we might be able to do, but the 20% latency isn't going to change significantly on the face of things.

We have an open ticket to look into this ( and at some point we'll try and put together the sample programs in a github repository (if that's not already done - I might've missed previous spikes done by Edsko or others) and investigate further.

One of the other (more experienced!) devs might be able to chip in and proffer a better explanation.


On 6 Feb 2013, at 13:27, kostirya at wrote:

> Haven’t you had a necessity to launch Haskell in no-threaded mode during the intense network data exchange? 
> I am getting the double performance penalty in threaded mode. But I must use threaded mode because epoll and kevent are available in the threaded mode only. 


> среда, 6 февраля 2013 г., 12:33:36 UTC+2 пользователь Tim Watson написал:
> Hello all, 
> It's been a busy week for Cloud Haskell and I wanted to share a few of 
> our news items with you all. 
> Firstly, we have a new home page at, 
> into which most of the documentation and wiki pages have been merged. Making 
> sassy looking websites is not really my bag, so I'm very grateful to the 
> various author's whose Creative Commons licensed designs and layouts made 
> it easy to put together. We've already had some pull requests to fix minor 
> problems on the site, so thanks very much to those who've contributed already! 
> As well as the new site, you will find a few of us hanging out on the 
> #haskell-distributed channel on freenode. Please do come along and join in 
> the conversation. 
> We also recently split up the distributed-process project into separate 
> git repositories, one for each component that makes up Cloud Haskell. This 
> was done partly for administrative purposes and partly because we're in the 
> process of setting up CI builds for all the projects. 
> Finally, we've moved from Github's issue tracker to a hosted Jira/Bamboo setup 
> at - pull requests are naturally still welcome 
> via Github! Although you can browse issues freely without logging in, you will 
> need to provide an email address and get an account in order to submit new ones. 
> If you have any difficulties logging in, please don't hesitate to contact me 
> directly, via this forum or the cloud-haskell-developers mailing list (on 
> google groups). 
> As always, we'd be delighted to hear any feedback! 
> Cheers, 
> Tim

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