svn commit: r247319 - in projects/calloutng/sys: kern sys

[Alexander Motin]

On 26.02.2013 17:28, Attilio Rao wrote:
> On Tue, Feb 26, 2013 at 4:25 PM, Alexander Motin <mav at freebsd.org> wrote:
>> Author: mav
>> Date: Tue Feb 26 15:25:43 2013
>> New Revision: 247319
>> URL: http://svnweb.freebsd.org/changeset/base/247319
>>
>> Log:
>>   Optimize callout_process() to use less variables and less conditions to
>>   implement the same logic.  Now it fits better into CPU registers, and
>>   according to PMC significntly reduces number of resource stalls, reducing
>>   consumed by it CPU time during usleep(1) benchmark by 30%.
> 
> Is that all improved i-cache capacity and improved dynamic branch
> prediction (hwpmc has counters for both FWIW)?

I-cache capacity I think is not significant there as the loop is quite
small. I believe it was branch misprediction, complicated by additional
latency of memory accesses. I haven't analyzed cause deeper, as PMC man
pages are not the most informative and easiest reading.

-- 
Alexander Motin