Date: Sun, 22 Feb 2015 11:37:09 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Daniel J Blueman <daniel@numascale.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Rafael David Tinoco <inaddy@ubuntu.com>, Peter Anvin <hpa@zytor.com>,
        Jiang Liu <jiang.liu@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Gema Gomez <gema.gomez-solano@canonical.com>,
        Christopher Arges <chris.j.arges@canonical.com>,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: smp_call_function_single lockups
Message-ID: <20150222103709.GA24818@gmail.com>
References: <54E99A8F.1080803@numascale.com>
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* Daniel J Blueman <daniel@numascale.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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