linux-kernel - Re: smp_call_function

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Message-ID: <20150222103709.GA24818@gmail.com>
Date:	Sun, 22 Feb 2015 11:37:09 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Daniel J Blueman <daniel@...ascale.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rafael David Tinoco <inaddy@...ntu.com>,
	Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	Christopher Arges <chris.j.arges@...onical.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: smp_call_function_single lockups


* Daniel J Blueman <daniel@...ascale.com> wrote:

> The Intel SDM [1] and AMD F15h BKDG [2] state that IPIs 
> are queued, so the wait_icr_idle() polling is only 
> necessary on PPro and older, and maybe then to avoid 
> delivery retry. This unnecessarily ties up the IPI 
> caller, so we bypass the polling in the Numachip APIC 
> driver IPI-to-self path.

It would be nice to propagate this back to the generic x86 
code.

> On Linus's earlier point, with the large core counts on 
> Numascale systems, I previously implemented a shortcut to 
> allow single IPIs to bypass all the cpumask generation 
> and walking; it's way down on my list, but I'll see if I 
> can generalise and present a patch series at some point 
> if interested?

I am definitely interested!

Thanks,

	Ingo
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