linux-kernel - Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer

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Message-ID: <20160823084735.GO10153@twins.programming.kicks-ass.net>
Date:   Tue, 23 Aug 2016 10:47:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Clark Williams <williams@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jon Masters <jcm@...hat.com>, Daniel Wagner <wagi@...om.org>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v2 0/4] tracing: Add Hardware Latency detector tracer

On Fri, Aug 19, 2016 at 09:36:41AM -0700, John Stultz wrote:
> On Fri, Aug 19, 2016 at 8:05 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > John, looks like 4ca22c2648f9 ("timekeeping: Add warnings when overflows
> > or underflows are observed") buggered things.
> 
> Oof. Apologies. I missed that the fast methods called that helper as well.
> 
> 
> Any objection to open-coding it for the fast method, like (sorry for
> the whitespace damage here):
> 
> @@ -401,7 +401,10 @@ static __always_inline u64
> __ktime_get_fast_ns(struct tk_fast *tkf)
>         do {
>                 seq = raw_read_seqcount_latch(&tkf->seq);
>                 tkr = tkf->base + (seq & 0x01);
> -               now = ktime_to_ns(tkr->base) + timekeeping_get_ns(tkr);
> +               now = ktime_to_ns(tkr->base);
> +
> +               now += clocksource_delta(tkr->read(tkr->clock),
> +                                        tkr->cycle_last, tkr->mask);
>         } while (read_seqcount_retry(&tkf->seq, seq));
> 
>         return now;
> 
> If not I'll get such a patch sorted, tested and tagged for -stable.

Works for me, Thomas?