linux-kernel - Re: [PATCH v2] X86: Hook apic vector allocation domain only when interrupt routing are set to ignore

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Message-ID: <20140427115036.GA22116@gmail.com>
Date:	Sun, 27 Apr 2014 13:50:36 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Oren Twaig <oren@...lemp.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Shai Fultheim <shai@...lemp.com>
Subject: Re: [PATCH v2] X86: Hook apic vector allocation domain only when
 interrupt routing are set to ignore


* Oren Twaig <oren@...lemp.com> wrote:

> Hi Ingo,
> 
> On 04/26/2014 09:09 AM, Ingo Molnar wrote:
> > I still don't see a clear explanation of what the _user_ saw and sees
> > before and after the change. What is the effect of the patch: correct
> > IRQ routing (i.e. before the change IRQs would end up on the wrong
> > CPU), lower overhead IRQ routing (i.e. before the change IRQ routing
> > overhead was more expensive), or something else?
> >
> > You don't spell this out clearly and it's a crucial piece of
> > information that comes before every other explanation.
> >
> I see.. I tried to explain the entire flow and that was confusing - I'll explain
> only the patch.
> 
> As you stated, in general, the patch corrects IRQ routing in case a vSMP
> Foundation box is detected but the Interrupt Routing Comply (IRC) is set to
> "comply".
> 
> Before the patch:
> When a vSMP Foundation box was detected and IRC was set to "comply", users (and
> kernel) couldn't effectively set the destination of the IRQs. This is because
> the hook inside vsmp_64.c always setup all CPUs as the IRQ destination using
> cpumask_setall() as the return value for IRQ allocation mask. Later, this
> "overrided" mask caused the kernel to set the IRQ destination to the lowest
> online CPU in the mask (CPU0 usually).
> 
> After the patch:
> When the IRC is set to "comply", Users (and kernel) can control the destination
> of the IRQs as we will not be changing the default
> "apic->vector_allocation_domain".

Much better, thanks!

	Ingo
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