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

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Message-ID: <56b36edb-1ff8-a154-d3c5-d2304e3554c0@gmail.com>
Date:   Wed, 13 May 2020 19:42:57 +0100
From:   Wojciech Kudla <wk.kernel@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>
Subject: Re: x86/smp: adding new trace points

On 13/05/2020 17:43, Thomas Gleixner wrote:
> Wojciech Kudla <wk.kernel@...il.com> writes:
>> On 13/05/2020 13:24, Thomas Gleixner wrote:
>>
>>> 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.
>>>
>>
>> Wrong vector, my bad.
>>
>> However 2) still stands in my opinion. We don't have "ipi raise" trace
>> point for x86.  RESCHEDULE_VECTOR, CALL_FUNCTION_SINGLE_VECTOR, as
>> well as TLB invalidation vectors are essentially
>> inter-processor-interrupts if I'm not mistaken.  Would a patch adding
>> such trace point be considered here?
> 
> Maybe.
> 
> Though that IPI tracing is inconsistent across architectures. I'm not
> really interested to have yet another x86 variant which is slightly
> different than anything else.
> 
> ARM and ARM64 share generic tracepoints for that, though the actual
> tracepoint invocation is in the architecture specific code.
> 
> If at all we really want to have the common IPIs which are required for
> SMP support covered by generic tracepoints and have them in the generic
> code and not sprinkled all over arch/*

How about we add ipi:ipi_raise trace points before:
- arch_send_call_function_single_ipi(), and 
- arch_send_call_function_ipi_mask()

Would that be a good starting point to introduce more generic IPI tracing?

Thanks,
Wojtek