[boost] Re: lightweight mutex for MacOS

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2004-01-29 15:18:35

On Jan 29, 2004, at 9:28 AM, Alexander Terekhov wrote:

> Get rid of yield.

Thanks for the suggestion!  New timing information:

+--------------------+-------+--------+------------+---------+
|                    |   OS  |   LWM  |LWM/no yield|   naive |
+--------------------+-------+--------+------------+---------+
| CFM      contested |  248  |  1.86  |    9.25    |   crash |
+--------------------+-------+--------+------------+---------+
| CFM    uncontested | 28.5  |  1.79  |    1.77    |   0.994 |
+--------------------+-------+--------+------------+---------+
| Mach-O   contested |  202  |  3.03  |    15.4    |  assert |
+--------------------+-------+--------+------------+---------+
| Mach-O uncontested | 3.26  |  1.69  |    1.76    |   0.800 |
+--------------------+-------+--------+------------+---------+

That lack of yield appears to produce a 400% performance drop for this 
particular test (contested variant) on these platforms.

I understand the potential for priority inversion, but for these 
performance gains, and for a "cheap fast mutex", the yield looks like a 
good deal to me.  I agree that for a more general purpose mutex other 
decisions might be made.

Thanks for the lwsync tip!  Alas, CodeWarrior does not currently 
support this instruction else I would've included  timings for that 
change too.

-Howard