linux-kernel - Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally

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Message-ID: <alpine.DEB.2.21.1910211658040.1904@nanos.tec.linutronix.de>
Date:   Mon, 21 Oct 2019 16:58:18 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Huacai Chen <chenhc@...ote.com>
cc:     Andy Lutomirski <luto@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        chenhuacai@...il.com, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Paul Burton <paul.burton@...s.com>, linux-mips@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data
 unconditionally

On Mon, 21 Oct 2019, Thomas Gleixner wrote:

> On Mon, 21 Oct 2019, Huacai Chen wrote:
> > @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> >  		cycles = __arch_get_hw_counter(vd->clock_mode);
> >  		ns = vdso_ts->nsec;
> >  		last = vd->cycle_last;
> > -		if (unlikely((s64)cycles < 0))
> > +		if (unlikely(cycles == U64_MAX))
> >  			return -1;
> 
> That used to create worse code than the weird (s64) type cast which has the
> same effect. Did you double check that there is no change?

It still does for 32bit.