Re: [PATCH v2 05/13] x86/irq: Reserve a per CPU IDT vector for posted MSIs

Re: [PATCH v2 05/13] x86/irq: Reserve a per CPU IDT vector for posted MSIs

[Andi Kleen]

Thomas Gleixner <tglx@linutronix.de> writes:

Dropping CC of a bazillion people and adding Arnaldo who owns perf trace
which has the vector decoding code.

> On Mon, Apr 15 2024 at 13:43, Jacob Pan wrote:
>> On Mon, 15 Apr 2024 11:53:58 -0700, Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
>>> On Thu, 11 Apr 2024 18:51:14 +0200, Thomas Gleixner <tglx@linutronix.de> wrote:
>>> > If we really care then we do it proper for _all_ of them. Something like
>>> > the uncompiled below. There is certainly a smarter way to do the build
>>> > thing, but my kbuild foo is rusty.  
>>> I too had the concern of the wasting system vectors, but did not know how
>>> to fix it. But now your code below works well. Tested without KVM in
>>> .config to show the gaps:
>>> 
>>> In VECTOR IRQ domain.
>>> 
>>> BEFORE:
>>> System: 46: 0-31,50,235-236,244,246-255
>>> 
>>> AFTER:
>>> System: 46: 0-31,50,241-242,245-255
>>> 
>>> The only gap is MANAGED_IRQ_SHUTDOWN_VECTOR(243), which is expected on a
>>> running system.
>>> 
>>> Verified in irqvectors.s: .ascii "->MANAGED_IRQ_SHUTDOWN_VECTOR $243
>>> 
>>> POSTED MSI/first system vector moved up from 235 to 241 for this case.
>>> 
>>> Will try to let tools/arch/x86/include/asm/irq_vectors.h also use it
>>> instead of manually copy over each time. Any suggestions greatly
>>> appreciated.
>>>
>> On a second thought, if we make system IRQ vector determined at compile
>> time based on different CONFIG options, will it break userspace tools such
>> as perf? More importantly the rule of not breaking userspace.
>
> tools/arch/x86/include/asm/irq_vectors.h is only used to generate the
> list of system vectors for pretty output. And your change already broke
> that.
>
> The obvious solution to that is to expose that list in sysfs for
> consumption by perf.
>
> But we don't have to do any of that right away. It's an orthogonal
> issue. Just waste the extra system vector to start with and then we can
> add the compile time dependend change on top if we really care about
> gaining back the vectors.
>
> Thanks,
>
>         tglx

Re: [PATCH v2 05/13] x86/irq: Reserve a per CPU IDT vector for posted MSIs

[Thomas Gleixner]

On Fri, Apr 19 2024 at 07:24, Andi Kleen wrote:
> Thomas Gleixner <tglx@linutronix.de> writes:
>
> Dropping CC of a bazillion people and adding Arnaldo who owns perf trace
> which has the vector decoding code.

He was already on Cc.