Re: [PATCH 0/2] cpustat: use atomic operations to read/update stats

From: Peter Zijlstra
Date: Fri Feb 22 2013 - 09:25:46 EST

On Fri, 2013-02-22 at 15:16 +0100, Ingo Molnar wrote:
> > I checked arch/x86/include/asm/atomic64_32.h and we use
> > cmpxchg8b for everything from _set() to _read(), which
> > translates into 'horridly stupendifyingly slow' for a number
> > of machines, but coherent.
> That's a valid concern - and cmpxchg8b is the only 64-bit op
> available on most 32-bit x86 CPUs which does not involve the
> FPU.
> Wondering how significant this range of x86 problem boxes will
> be by the time any of these changes reaches upstream and distros
> - and how much 'horridly stupendifyingly slow' is in terms of
> cycles expended.

On the !x86 side of things we're implementing (generic) atomic64 using
hashed spinlocks, so there too using a single spinlock around the
entire data structure is a complete win.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at