From: SASADA Koichi <ko1@...>
Date: 2014-03-13T22:29:46+09:00
Subject: [ruby-core:61466] Re: [REJECT?] xmalloc/xfree: reduce atomic ops w/ thread-locals

Hi Eric,

Currently, `malloc_increase' (and so on) only a *hint*.

So I think we can eliminate atomic instruction simply. What do you think
about?

# basically, GVL protects multi-threads parallel update of such values.
# this atomic operations only for call_without_gvl().
# so it is minor case.


(2014/03/12 9:06), Eric Wong wrote:
> I'm unsure about this.  I _hate_ the extra branches this adds;
> and most of our benchmarks don't show an improvement.  But this
> seems like an obvious experiment, so maybe somebody else would've
> tried it if I didn't at least publish it here.
> 
> 
> Atomic operations are expensive, so use thread-local counters and
> only perform atomic operations when the local counters hit a
> predefined limit (currently 16K).
> 
> This gives a ~12% speedup to the bm_so_count_words.rb benchmark
> which does many small mallocs.  This pattern is common in some Ruby
> scripts doing text processing, so maybe it is worth doing.
> 
> Unfortunately, this adds more branches, increases code size, and
> hurts accuracy of GC accounting in multithreaded programs.  Some
> benchmarks are slower as a result.
> 
> Full benchmark results in the full patch:
> 
> http://bogomips.org/ruby.git/patch?id=8271ec7b977
> 	git://80x24.org/ruby.git gc-lessatomic
> 


-- 
// SASADA Koichi at atdot dot net