linux-kernel - Re: [patch] generic-ipi: remove kmalloc, cleanup

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Message-Id: <200902140746.45320.rusty@rustcorp.com.au>
Date:	Sat, 14 Feb 2009 07:46:44 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...x.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"rt-users" <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Carsten Emde <ce@...g.ch>, Clark Williams <williams@...hat.com>
Subject: Re: [patch] generic-ipi: remove kmalloc, cleanup

On Thursday 12 February 2009 22:39:14 Peter Zijlstra wrote:
> So it put in unconditionally, how about this?
> 
> 
> --
> Subject: generic-smp: remove single ipi fallback for smp_call_function_many()
> 
> In preparation of removing the kmalloc() calls from the generic-ipi code
> get rid of the single ipi fallback for smp_call_function_many().
> 
> Because we cannot get around carrying the cpumask in the data -- imagine
> 2 such calls with different but overlapping masks -- put in a full mask.

OK, if you really want this, please just change it to:
	unsigned long cpumask_bits[BITS_TO_LONGS(CONFIG_NR_CPUS)];

The 'struct cpumask' will be undefined soon when CONFIG_CPUMASK_OFFSTACK=y,
which will prevent assignment and declaration on stack.

I'd be fascinated to see perf numbers once you kill the kmalloc.  Because
this patch will add num_possible_cpus * NR_CPUS/8 bytes to the kernel which
is something we're trying to avoid unless necessary.

Thanks,
Rusty.
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