linux-kernel - Re: [PATCH] [12/58] x86_64: Add vDSO for x86-64 with gettimeofday/clock

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Date:	Tue, 21 Aug 2007 09:25:01 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Andi Kleen <ak@...e.de>
Cc:	patches@...-64.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] [12/58] x86_64: Add vDSO for x86-64 with
	gettimeofday/clock_gettime/getcpu

On Thu, 2007-07-19 at 11:54 +0200, Andi Kleen wrote:
> +
> +static noinline int do_realtime(struct timespec *ts)
> +{
> +       unsigned long seq, ns;
> +       do {
> +               seq = read_seqbegin(&gtod->lock);
> +               ts->tv_sec = gtod->wall_time_sec;
> +               ts->tv_nsec = gtod->wall_time_nsec;
> +               ns = vgetns();
> +       } while (unlikely(read_seqretry(&gtod->lock, seq)));
> +       timespec_add_ns(ts, ns);
> +       return 0;
> +} 

Some thoughts ,

In the -mm kernel there is some debugging that gets injected into the
likely/unlikely macros .. If they get called from userspace it causes a
hang .. We might want to add some new set of macros to specifically
denote that they are called from userspace, not just likely/unlikely but
all the macros so we don't get mixed usage ..

Daniel

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