signifanctly slowdown of FreeBSD 8.0-CURRENT/amd64

[O. Hartmann]

bf wrote:
>
> --- On Sat, 5/30/09, Kip Macy <kmacy at freebsd.org> wrote:
>
>   
>> From: Kip Macy <kmacy at freebsd.org>
>> Subject: Re: signifanctly slowdown of FreeBSD 8.0-CURRENT/amd64
>> To: "bf" <bf2006a at yahoo.com>
>> Cc: freebsd-current at freebsd.org, attilio at freebsd.org, ohartman at mail.zedat.fu-berlin.de
>> Date: Saturday, May 30, 2009, 11:55 PM
>>     
>>> I'm running the r193133 amd64 with a custom kernel and
>>>       
>> all debugging off
>>     
>>> on an AMD Athlon64 3400+ single-core, and I haven't
>>>       
>> noticed any significant
>>     
>>> slowing, although I haven't been doing any systematic
>>>       
>> benchmarking.
>>     
>>> What would be the penalties of running an SMP -CURRENT
>>>       
>> kernel on
>>     
>>> single-core hardware with no hyperthreading? Can
>>>       
>> anyone quantify the
>>     
>>> typical added overhead?  Or, counterintuitively,
>>>       
>> would an SMP kernel
>>     
>>> be better in some ways?
>>>
>>>       
>> He is trying to diagnose if the problem was introduced by
>> enabling
>> adaptive spinning on sx locks. They're only enabled on SMP
>> kernels.
>>
>> Cheers,
>> Kip
>>
>>     
>
> So I inferred from his request to have Oliver (the original poster)
> revert r193011.  But it seems unlikely that this is solely or even mostly
> responsible for the slowdown, as Oliver reported that it first began
> to occur several weeks ago, and Attilio only committed r193011 on Friday
> -- unless Oliver independently added ADAPTIVE_SX to his custom kernel
> a few weeks ago.  In any event, I'm still interested in any reports of
> the relative performance of SMP vs. UP kernels on UP hardware that 
> anyone is able to share.
>
> Thanks,
>          b.
>
>
>       
>   
Would the addition of

ADAPTIVE_SX

to a SMP kernel or kernel of any kind have perfomance issues, also
performance gains?