linux-kernel - Re: [patch V6 01/37] tracing/hwlat: Use ktime_get_mono_fast

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Message-ID: <871rnf7g61.fsf@nanos.tec.linutronix.de>
Date:   Tue, 19 May 2020 23:45:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <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>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>
Subject: Re: [patch V6 01/37] tracing/hwlat: Use ktime_get_mono_fast_ns()

Steven Rostedt <rostedt@...dmis.org> writes:
> On Sat, 16 May 2020 01:45:48 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
>> +	if (enter)
>> +		nmi_ts_start = ktime_get_mono_fast_ns();
>> +	else
>> +		nmi_total_ts += ktime_get_mono_fast_ns() - nmi_ts_start;
>>  
>>  	if (enter)
>>  		nmi_count++;
>> @@ -165,20 +155,22 @@ void trace_hwlat_callback(bool enter)
>>   * Used to repeatedly capture the CPU TSC (or similar), looking for potential
>>   * hardware-induced latency. Called with interrupts disabled and with
>>   * hwlat_data.lock held.
>> + *
>> + * Use ktime_get_mono_fast() here as well because it does not wait on the
>> + * timekeeping seqcount like ktime_get_mono().
>
> When doing a "git grep ktime_get_mono" I only find
> ktime_get_mono_fast_ns() (and this comment), so I don't know what to compare
> that to. Did you mean another function?

Yeah. I fatfingered the comment. The code uses ktime_get_mono_fast_ns().

> The rest looks fine (although, I see other things I need to clean up in
> this code ;-)

Quite some ...

Thanks,

        tglx