linux-kernel - Re: [PATCH 00/11] x86: cpumask: some more cpumask cleanups

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Date:	Tue, 06 Jan 2009 18:50:26 -0800
From:	Mike Travis <travis@....com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, Cliff Wickman <cpw@....com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Jes Sorensen <jes@....com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/11] x86: cpumask: some more cpumask cleanups - flush_tlb_*

Rusty Russell wrote:
> On Tuesday 06 January 2009 14:19:35 Mike Travis wrote:
>> Ingo Molnar wrote:
>>> Quite good! Can we fix those TLB flush cpumask uses too?
>> Here is one proposal.
> 
> Here's what I had.  It's untested though...
> 
> x86: change flush_tlb_others to take a const struct cpumask *. FIXME: REVIEW
> 
> This is made a little more tricky by uv_flush_tlb_others which
> actually alters its argument, for an IPI to be sent to the remaining
> cpus in the mask.
> 
> I solve this by allocating a cpumask_var_t for this case and falling back
> to IPI should this fail.

I thought about this but I wondered if we wanted to add the overhead of a kmalloc
call for every tlb flush?  For a UV system, simultaneous flushes will be quite common,
so introducing two kmalloc's in the path could really hamper performance.

Thanks,
Mike
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