linux-kernel - Re: smp_call_function

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Message-ID: <CAMiJ5CU+rvQr-_Ejd3m3ha3HsiSKu0Sq_fTaE2Ws_c_01=qbLQ@mail.gmail.com>
Date:	Thu, 19 Feb 2015 14:32:04 -0200
From:	Rafael David Tinoco <inaddy@...ntu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>,
	chris.j.arges@...onical.com,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: smp_call_function_single lockups

For the host, we are using "intremap=no_x2apic_optout
intel_idle.max_cstate=0" for cmdline. It looks like that DL360/DL380
Gen8 firmware still asks to optout from x2apic but HP engineering team
said that using x2apic for Gen8 would be ok (intel_idle causes these
servers to generate NMIs when idling, probably related to packed
c-states and this server's dependency on acpi tables for c-state).

Feb 19 08:21:28 derain kernel: [    3.504676] Enabled IRQ remapping in
x2apic mode
Feb 19 08:21:28 derain kernel: [    3.565451] Enabling x2apic
Feb 19 08:21:28 derain kernel: [    3.602134] Enabled x2apic
Feb 19 08:21:28 derain kernel: [    3.637682] Switched APIC routing to
cluster x2apic.

On Thu, Feb 19, 2015 at 2:26 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Thu, Feb 19, 2015 at 7:42 AM, Rafael David Tinoco <inaddy@...ntu.com> wrote:
>>
>> Same environment as before: Nested KVM (2 vcpus) on top of Proliant
>> DL380G8 with acpi_idle and no x2apic optout.
>
> Btw, which apic model does that end up using? Does "no x2apic optout"
> mean you're using the x2apic?
>
> What does "dmesg | grep apic" report? Something like
>
>     Switched APIC routing to cluster x2apic.
>
> or what?
>
> Side note to the apic guys: I think the "single CPU" case ends up
> being one of the most important ones, but the stupid APIC model
> doesn't allow that, so sending an IPI to a single CPU ends up being
> "send a mask with a single bit set", and then we have that horrible
> "for_each_cpu(cpu, mask)" crap.
>
> Would it make sense to perhaps add a "send_IPI_single()" function
> call, and then for the APIC models that always are based on masks, use
> a wrapper that just does that "cpumask_of(cpu)" thing..
>
> Hmm?
>
>                        Linus
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