Re: Cost of atomic operations on new hardware

["Paul E. McKenney" <paulmck@linux.ibm.com>]

On Fri, Apr 26, 2019 at 07:06:10AM -0400, Elad Lahav wrote:
> Hello,
> 
> Section 3.1.3 contains the following statement:
> 
> "Fortunately, CPU designers have focused heavily on atomic operations,
> so that as of early 2014 they have greatly reduced their overhead."
> 
> My experience with very recent hardware is that the *relative* cost of
> atomic operations has actually increased significantly. It seems that
> hardware designers, in their attempt to optimize performance for
> certain workloads, have produced hardware in which the "anomalous"
> conditions (atomic operations, cache misses, barriers, exceptions)
> incur much higher penalties than in the past. I assume that this is
> primarily the result of more intensive speculation and prediction.

Some of the early 2000s systems had -really- atomic operations, but I
have not kept close track since 2014.

How would you suggest that this be measured?  Do you have access to
a range of hardweare that would permit us to include something more
definite and measurable?

							Thanx, Paul