svn commit: r230201 - head/lib/libc/gen

[David Xu]

On 2012/1/20 0:55, Bruce Evans wrote:
> On Thu, 19 Jan 2012, John Baldwin wrote:
>
>> On Thursday, January 19, 2012 12:57:50 am David Xu wrote:
>>> rdtsc() may not work on SMP, so I have updated it to use clock_gettime
>>> to get total time.
>>> http://people.freebsd.org/~davidxu/bench/semaphore2/
>>> <http://people.freebsd.org/%7Edavidxu/bench/semaphore2/>
>>>
>>> Still, lfence is a lot faster than atomic lock.
>
> I hope it does non-microbenchmarks.  IIRC, jhb found that it was
> actually slower in some cases.  I only did micro-benchmarks on Athlon64.

It depends on hardware, if it is a large machine with lots of cpu,
a small conflict on dual-core machine can become a large conflict
on large machine because it is possible more cpus are now
running same code which becomes a bottleneck. On a large machine
which has 1024 cores, many code need to be redesigned.