linux-kernel - Re: [RFC][PATCH 3/3] x86/entry, ORC: Teach objtool/unwind

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Message-ID: <87sggak3yf.fsf@nanos.tec.linutronix.de>
Date:   Fri, 08 May 2020 14:26:32 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, luto@...nel.org
Subject: Re: [RFC][PATCH 3/3] x86/entry, ORC: Teach objtool/unwind_orc about stack irq swizzles

Peter Zijlstra <peterz@...radead.org> writes:

> On Thu, May 07, 2020 at 11:24:49PM +0200, Thomas Gleixner wrote:
>> But over our IRC conversation I came up with a 3rd variant:
>> 
>>   For most of the vectors the indirect call overhead is just noise, so
>>   we can run them through the ASM switcher, but for the resched IPI
>>   we can just use a separate direct call stub in ASM.
>
> Are we sure the rat-poison crap is noise for all the other system
> vectors? I suppose it is for most since they'll do indirect calls
> themselves anyway, right?

We have different categories:

 1) Uninteresting

    SPURIOUS_APIC_VECTOR, ERROR_APIC_VECTOR, THERMAL_APIC_VECTOR,
    THRESHOLD_APIC_VECTOR, REBOOT_VECTOR, DEFERRED_ERROR_VECTOR

 2) Indirect call poisoned

    LOCAL_TIMER_VECTOR
    X86_PLATFORM_IPI_VECTOR
    IRQ_WORK_VECTOR
    HYPERV_STIMER0_VECTOR
    HYPERVISOR_CALLBACK_VECTOR
    POSTED_INTERRUPT_WAKEUP_VECTOR.
    CALL_FUNCTION_VECTOR
    CALL_FUNCTION_SINGLE_VECTOR
    
 3) Quick

    RESCHEDULE_VECTOR

    POSTED_INTR_VECTOR
    POSTED_INTR_NESTED_VECTOR

        These two postit ones are weird because they are both empty and
        just increment different irq counts.

    HYPERV_REENLIGHTENMENT_VECTOR

        schedules delayed work, i,e. arms a timer which should be
        straight forward, but does it matter?

 4) Others

    UV_BAU_MESSAGE - The TLB flushes are probably more expensive than
                     ratpoutine

Hmm?

Thanks,

        tglx