[tesla-dev] P-state statistics issue

[Eric Saxe]

Alexander Kolbasov wrote:
> I doscussed this with Eric, just wanted to have some online record. 
>
>     Li> DTRACE_PROBE2(cpu_change_speed, processorid_t, cpudsp->cpu_id,
>     Li> 	uint_t, new_spd->speed);
>     Li> DTRACE_PROBE2(cpu_change_speed, processorid_t, cpudsp->cpu_id,
>     Li> 	uint_t, new_spd->speed);
>
> In generl it is not a good idea to dereference pointers in DTRACE SDT
> probes since this will increase disabled probe effect. It is better to
> provide raw pointers (preferably available on the stack already) and
> then have translators defined that will defer pointer dereference to
> the time when the probe is enabled. 
>   
Aubrey was keen enough to point out that the "old speed" pointer (which 
I added) could be NULL, if the CPU has never undergone a CPU speed 
change. I was wondering if it would be possible to have the current 
speed initialized (perhaps at attach / initialization time)? That would 
save having to worry about having an uninitialized current speed 
throughout much of the code, including the DTrace probe / translator 
implementation.

-Eric