linux-kernel - Re: [patch V4 part 1 14/36] x86/entry: Get rid of ist_begin/end_non

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Message-ID: <877dxdy211.fsf@nanos.tec.linutronix.de>
Date:   Fri, 15 May 2020 11:34:50 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        paulmck <paulmck@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>, rostedt <rostedt@...dmis.org>,
        "Joel Fernandes\, Google" <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 1 14/36] x86/entry: Get rid of ist_begin/end_non_atomic()

Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:

> ----- On May 5, 2020, at 9:16 AM, Thomas Gleixner tglx@...utronix.de wrote:
>
>> This is completely overengineered and definitely not an interface which
>> should be made available to anything else than this particular MCE case.
>
> This patch introduces a significant change under the radar (not explained
> in the changelog): it turns preempt_enable_no_resched() into preempt_enable().
>
> Why, and why was it a no_resched() in the first place ? Was it for performance
> or correctness reasons ?

_no_resched() is an optimization when in code which cannot schedule
anyway. But #MC is definitely not a performance critical hotpath.

So yes, it's a change but really not significant.

>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>> ---
< Remove useless gunk >

Can you please trim your replies?

Thanks,

        tglx