Re: (*(unsigned long *)&jiffies)++;

Manfred Spraul (manfreds@colorfullife.com)
Thu, 6 Jan 2000 18:00:47 +0100

From: "Tigran Aivazian" <tigran@sco.COM>
> On Thu, 6 Jan 2000, Petko Manolov wrote:
> > Exactly.
> > "(*(unsigned long *)&jiffies)++" did just "incl jiffies"
> > at the time and in the place you write it.
>
> Ok. Why is it not done for lost_ticks and lost_ticks_system?
>
I don't know. I just checked my source archive: linux-1.2.13 uses
"jiffies++", and 2.0.38 uses "(*(...))".

I don't know why this cast was added, but it doesn't enforce atomicity on
SMP computers. _If_ we really need the atomicity, then something like this
could fix the problem:

- unsigned long volatile jiffies = 0;
+atomic_t atomic_jiffies = ATOMIC_INIT(0);

+ #define INC_JIFFIES() atomic_inc(&atomic_jiffies);
+ #defien ADD_JIFFIES(inc) atomci_add(&atomic_jiffies,inc);
+ #define jiffies ((unsigned long) atomic_get(&atomic_jiffies));

Warning: I never tried that, I didn't check if it will be correct on 64-bit
archs, ...

--
    Manfred




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