[Haskell-cafe] When are MVars better than STM?

Yuras Shumovich shumovichy at gmail.com
Sun Jan 24 15:09:32 UTC 2016

On Sun, 2016-01-24 at 17:46 +1100, Thomas Koster wrote:
> 2. When given two capabilities (+RTS -N2), MVars are suddenly an
> order
> of magnitude slower than with just one capability. Why?

One possible explanation is closure locking which is not performed when
there is only one capability. In my quick measurements it gives 40%
speedup: https://ghc.haskell.org/trac/ghc/ticket/693#comment:9

More information about the Haskell-Cafe mailing list