Thread behavior in 7.8.3

[Michael Jones]

Ben,

I am using Bas van Dijk’s usb, and I am past the -threading issue by using the latest commit.

I don’t have any easy way of making comparisons between 7.6 and 7.8 productivity, but from oscilloscope activity, I can’t see any difference. The only difference I see is the thread scheduling on 7.8 for -N1 vs -N2/4.

If —sstderr gives some notion of productivity, I’ll have to do an experiment between -N1 and -N2/4. Unchartered territory for me. I’ll setup and experiment tonight.

I am not familiar with strace. I’ll fix that soon.

Mike

On Oct 29, 2014, at 10:24 AM, Ben Gamari <bgamari.foss at gmail.com> wrote:

> Michael Jones <mike at proclivis.com> writes:
> 
>> I have a general question about thread behavior in 7.8.3 vs 7.6.X
>> 
>> I moved from 7.6 to 7.8 and my application behaves very differently. I
>> have three threads, an application thread that plots data with
>> wxhaskell or sends it over a network (depends on settings), a thread
>> doing usb bulk writes, and a thread doing usb bulk reads. Data is
>> moved around with TChan, and TVar is used for coordination.
>> 
> Are you using Bas van Dijk's `usb` library by any chance? If so, you
> should be aware of this [1] issue.
> 
>> When the application was compiled with 7.6, my stream of usb traffic
>> was smooth. With 7.8, there are lots of delays where nothing seems to
>> be running. These delays are up to 40ms, whereas with 7.6 delays were
>> a 1ms or so.
>> 
>> When I add -N2 or -N4, the 7.8 program runs fine. But on 7.6 it runs
>> fine without with -N2/4.
>> 
>> The program is compiled -O2 with profiling. The -N2/4 version uses
>> more memory, but in both cases with 7.8 and with 7.6 there is no space
>> leak.
>> 
> Have you looked at the RTS's output when run with `+RTS -sstderr`?
> Is productivity any different between the two tests?
> 
>> I tired to compile and use -ls so I could take a look with
>> threadscope, but the application hangs and writes no data to the file.
>> The CPU fans run wild like it is in an infinite loop.
>> 
> Oh dear, this doesn't sound good at all. Have you tried getting a
> backtrace out of gdb? Usually this isn't terribly useful but in this
> case since the event log is involved it might be getting stuck in the RTS
> which should give a useful backtrace. If not, perhaps strace will give
> some clues as to what is happening (you'll probably want to hide
> SIGVTALM to improve signal/noise)?
> 
> Cheers,
> 
> - Ben
> 
> 
> [1] https://github.com/basvandijk/usb/issues/7