Luke Kenneth Casson Leighton wrote:
On Mon, Oct 20, 2014 at 2:34 PM, Howard Chu <h...@symas.com> wrote:
I can probably use taskset or something similar to restrict a process to a
particular set of cores. What exactly do you have in mind?

  keeping the writers and readers proposed test, but onto the same 8
cores only, running:

Well in the meantime, the 32/32 test finished:

Writers         Run Time                                CPU %   Context 
Switches        Write   Read                    Run Time                        
CPU %
        Wall            User            Sys                     Vol             
Invol                   Wall            User            Sys     
1       10:01.38        00:09:34.90     00:00:25.80     99      9               
2040    27160   5877894 10:00.68        05:19:03.44     00:00:35.34     3192
2       10:01.38        00:09:15.15     00:02:41.94     119     14397526        
2955    24012   6150801 10:00.67        05:19:00.96     00:00:38.23     3192
4       10:01.34        00:09:06.93     00:02:46.94     118     14246971        
8545    23795   6067928 10:00.68        05:18:59.65     00:00:39.52     3192
8       10:01.49        00:09:04.22     00:02:53.09     119     14011236        
10850   23589   5961381 10:00.69        05:18:56.82     00:00:42.54     3192
16      10:01.64        00:09:07.32     00:02:53.09     119     13787738        
20049   23670   5966794 10:00.68        05:18:59.13     00:00:40.35     3192
32      10:01.78        00:09:04.29     00:02:58.40     120     13205576        
27847   23337   5959624 10:00.70        05:19:00.54     00:00:39.46     3192

The timings on the left are for the writer process; the reader process
is on the right. You were right, the number of writers is largely
irrelevant because they're all waiting most of the time. There's a
huge jump in System CPU time from 1 writer to 2 writers, because with
only 1 writer the mutex is uncontended and essentially zero-cost. As
more writer threads are added, the System CPU time will rise.

The readers are basically unaffected by the number of writers.

--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/

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