[Openais] clock_gettime(2) notes...

[Steven Dake]

We need a MONOTONIC clock.  Looks like CLOCK_MONOTONIC_FAST appears to
be the best choice for us, since we don't care about high precision (10
msec precision is good enough).

Thanks for the benchmarks.

Regards
-steve

On Tue, 2009-07-21 at 11:42 -0700, Sean Chittenden wrote:
> re: clock_gettime(2).  I have a few random things to add there that  
> came out of some benchmarking that I did about a year ago for FreeBSD  
> and is of some relevance.  Issues regarding the correctness of yet- 
> another-clock_id aside, on FreeBSD CLOCK_REALTIME_FAST is ridiculously  
> fast compared to CLOCK_REALTIME.  I don't know what degree of  
> precision you're looking for in these time calls since  
> CLOCK_REALTIME_FAST only gets updated once a HZ, but it's a pretty  
> significant speedup.
> 
> The URL to the full post is below, but the specific excerpts from the  
> benchmark can be seen here:
> 
> % ./bench_time 9079882 | sort -rnk1
> Timing micro-benchmark.  9079882 syscall iterations.
> Avg. us/call    Elapsed     Name
> 9.322484    84.647053       gettimeofday(2)
> 8.955324    81.313291       time(3)
> 8.648315    78.525684       clock_gettime(2/CLOCK_REALTIME)
> 8.598495    78.073325       clock_gettime(2/CLOCK_MONOTONIC)
> 0.674194    6.121600        clock_gettime(2/CLOCK_PROF)
> 0.648083    5.884515        clock_gettime(2/CLOCK_VIRTUAL)
> 0.330556    3.001412        clock_gettime(2/CLOCK_REALTIME_FAST)
> 0.306514    2.783111        clock_gettime(2/CLOCK_SECOND)
> 0.262788    2.386085        clock_gettime(2/CLOCK_MONOTONIC_FAST)
> Last value from gettimeofday(2): 1212380080.620649
> Last value from time(3): 1212380161
> Last value from clock_gettime(2/CLOCK_VIRTUAL): 2.296430000
> Last value from clock_gettime(2/CLOCK_SECOND): 1212380338.000000000
> Last value from clock_gettime(2/CLOCK_REALTIME_FAST):  
> 1212380243.461081040
> Last value from clock_gettime(2/CLOCK_REALTIME): 1212380240.459788612
> Last value from clock_gettime(2/CLOCK_PROF): 185.560343000
> Last value from clock_gettime(2/CLOCK_MONOTONIC_FAST): 5747219.271879584
> Last value from clock_gettime(2/CLOCK_MONOTONIC): 5747216.886509281
> 
> http://sean.chittenden.org/news/2008/06/01/
> 
> Random drive-by $0.02. -sc
> 
> 
> --
> Sean Chittenden
> sean at chittenden.org
> 
> 
> 
> 
> 
> 
> --
> Sean Chittenden
> sean at chittenden.org
> 
> 
> 
> _______________________________________________
> Openais mailing list
> Openais at lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/openais