Re: Intel P6 vs P7 system call performance

[H. Peter Anvin]

Benjamin LaHaise wrote:
> On Tue, Dec 17, 2002 at 10:57:29AM -0800, Ulrich Drepper wrote:
> 
>>But this is exactly what I expect to happen.  If you want to implement
>>gettimeofday() at user-level you need to modify the page.  Some of the
>>information the kernel has to keep for the thread group can be stored in
>>this place and eventually be used by some uerlevel code  executed by
>>jumping to 0xfffff000 or whatever the address is.
> 
> 
> You don't actually need to modify the page, rather the data for the user 
> level gettimeofday needs to be in a shared page and some register (like 
> %tr) must expose the current cpu number to index into the data.  Either 
> way, it's an internal implementation detail for the kernel to take care 
> of, with multiple potential solutions.
> 

That's not the problem... the problem is that the userland code can get
preempted at any time and rescheduled on another CPU.

	-hpa