ntdll: Change NtQuerySystemInformation to return 100ns ticks for SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION info class (try 4)

[Chris Robinson]

On Sunday, December 12, 2010 2:19:42 pm Louis Lenders wrote:
> +#define USER_HZ_TO_TICKSPERSEC(x,y) (ULONGLONG)10000000 * x / y

I'd recommend adding proper parenthesis, to avoid potential problems with 
order-of-operations.

#define USER_HZ_TO_TICKSPERSEC(x,y) ((ULONGLONG)10000000 * (x) / (y))

That way it won't break if you do math in the argument for some reason, like 
with
USER_HZ_TO_TICKSPERSEC(val+1, user_hz)
or
USER_HZ_TO_TICKSPERSEC(val, user_hz*2)

> +                    static long user_hz;
> +
> +                    user_hz = sysconf(_SC_CLK_TCK);

There's no real point to making it static if you're always going to (re)set 
the variable. It would be better to just make the call once:

static long user_hz;

i(user_hz == 0)
    user_hz = sysconf(_SC_CLK_TCK);


You could also make it an inline function to avoid making user_hz a parameter:

/* Convert system clock to 100ns tics */
static long user_hz;
static inline ULONGLONG ClockToTics(ULONGLONG val)
{
    i(user_hz == 0)
        user_hz = sysconf(_SC_CLK_TCK);
    return val * 10000000 / user_hz;
}
...
sppi->IdleTime.QuadPart = ClockToTics(idle);
sppi->KernelTime.QuadPart = ClockToTics(sys);
...etc...

Though I'll defer judgement to others as to what's better.