linux-kernel - Re: x86/smp: adding new trace points

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Message-ID: <87y2pw2fav.fsf@nanos.tec.linutronix.de>
Date:   Wed, 13 May 2020 14:24:40 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Wojciech Kudla <wk.kernel@...il.com>, linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org
Subject: Re: x86/smp: adding new trace points

Wojciech Kudla <wk.kernel@...il.com> writes:
> I was trying to trace some IPIs (remote tlb shootdowns in this case) and noticed that:
>
> 1) irq_vectors:x86_platform_ipi_entry and irq_vectors:x86_platform_ipi_exit are not hit at all for my case. The backtrace on the receiving CPU:
>
> 0xffffffff81079535	flush_tlb_func_common.constprop.10+0x105/0x220 [kernel]
> 0xffffffff81079681	flush_tlb_func_remote+0x31/0x40 [kernel]
> 0xffffffff8111f76c	flush_smp_call_function_queue+0x4c/0xf0 [kernel]
> 0xffffffff81120253	generic_smp_call_function_single_interrupt+0x13/0x30 [kernel]
> 0xffffffff81a030c6	smp_call_function_single_interrupt+0x36/0xd0 [kernel]
> 0xffffffff81a02679	call_function_single_interrupt+0xa9/0xb0 [kernel]
>
> I would expect that we would hit those trace point somewhere around
> call_function_single_interrupt()

Why would the SMP call function single interrupt go through the
PLATFORM_IPI_VECTOR? It goes as the name says through the
CALL_FUNCTION_SINGLE_VECTOR.

Thanks,

        tglx