linux-kernel - Re: local_add

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Date:	Fri, 19 Dec 2008 16:24:45 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	David Miller <davem@...emloft.net>, rostedt@...dmis.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	paulus@...ba.org, benh@...nel.crashing.org,
	linux-ia64@...r.kernel.org, linux-s390@...r.kernel.org,
	Christoph Lameter <christoph@...eter.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Martin Bligh <mbligh@...gle.com>
Subject: Re: local_add_return

On Friday 19 December 2008 14:05:14 Mathieu Desnoyers wrote:
> * Rusty Russell (rusty@...tcorp.com.au) wrote:
> But can we turn what you call "nmi_safe_t" into "local_atomic_t" then ?
> Because we have to specify that this type must only be used as part of
> per-cpu data with preemption disabled, and we also specify that it is
> atomic.
> 
> Plus, nmi_safe_t does not make much sense on architectures without NMIs,
> where we sometimes disable interrupts to make the modification "atomic"
> wrt all other interrupts that can happen.

But those archs can use local_t.  I don't like either name local_t nor
atomic_local_t, but renaming sucks too.

OK, how about a different approach?  Since there's really only one case
where we need this local_t property outside arch-specific code, how about
we define ARCH_LOCAL_T_TRACE_SAFE for x86?

Then some trace-specific typedef like "trace_counter_t" which goes to local_t
or atomic_(long?)_t?

Should be a simple patch and pretty clear.

Thanks,
Rusty.
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