Re: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* H. Peter Anvin (hpa@zytor.com) wrote:
> Mathieu Desnoyers wrote:
>> Sure, here are the updated tables. Basically, they show no significant
>> difference between the NOP and the DS segment selector prefix
>> approaches.
>
> Actually, unless I have blown my T-test completely, they show with a 80% 
> and 74% confidence (respective for the two benchmarks) that the DS case is 
> slightly *better* (0.26% and 0.20% better, respective), which makes it a 
> no-brainer.  Doing around 10 runs of each is likely to confirm this 
> conclusion by pushing it into the 90+% interval.
>

Yes, I think you are right.

> Note that since the difference is so small, and so can also be due to some 
> kind of systematic error (lower ambient temperature during the DS run 
> making the disk drive slightly faster, what have you.)
>

I doubt it, because I made a "cache priming" run before the tests, which
made sure the data was all populated in memory. But yeah, having
different cpu clock calibration values/cpu clock frequency between
reboots could also cause that kind of difference.

Mathieu

> 	-hpa

-- 
Mathieu Desnoyers
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