Re: [discuss] Re: [PATCH] x86-64: Fix bad assumption that dualcore cpus have synced TSCs

[Jonas Oreland <jonas@mysql.com>]

Ray Bryant wrote:
> On Wednesday 21 September 2005 10:04, Andi Kleen wrote:
> 
> 
>>We handle this, but single socket dual core was special cased because
>>I was told previously it should be ok.
>>
>>-Andi
> 
> 
> AFAIK there is a processor state bit that enables/disables this behavior.
> Apparently some BIOS's are setting this one way for desktop systems and the 
> other way for servers.   If it is thought to be important I can track that 
> down and see if it can be externally documented.  (It may actually be in the 
> bios and kernel developer guide...)
> 

Hi,

This would be very good (for us single socket dual core users)
I tried a very small benchmark:

clock_gettime(CLOCK_REALTIME): elapsed 7336657 -> 733.665700ns/call
clock_gettime(CLOCK_PROCESS_CPUTIME_ID): elapsed 763247 -> 76.324700ns/call

It's a factor 10 faster if the TSC were to be in sync.

/Jonas
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