Oops, sorry, only just now seen this. It seems my overly aggressive filters
couldn't decide where to put the email :)
I do agree to some extend with this. I'd prefer if I made a mistake for my
system not to hang. The one downside to this default though is that you
can't just hand a program over to user and have it run at full capabilities.
If it possible to set this from inside a program? My guess is no, since by
the time you get to main the rts is already initialized?
Would a useful alternative be to provide a compile flag that would change
the default? e.g. opt-in? Since now there is a small burden on the end user.
Cheers,
Tamar
On Sat, Oct 8, 2016 at 5:55 PM, Ben Gamari
lonetiger@gmail.com writes:
Hi All,
A user on https://ghc.haskell.org/trac/ghc/ticket/11054 has asked why -N -qa isn’t the default for -threaded.
I'm not sure that scheduling on all of the cores on the user's machine by default is a good idea, especially given that our users have learned to expect the existing default. Enabling affinity by default seems reasonable if we have evidence that it helps the majority of applications, but we would first need to introduce an additional flag to disable it.
In general I think -N1 is a reasonable default as it acknowledges the fact that deploying parallelism is not something that can be done blindly in many (most?) applications. To make effective use of parallelism the user needs to understand their hardware, their application, and its interaction with the runtime system and configure the RTS appropriately.
Of course, this is just my two-cents.
Cheers,
- Ben