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Date: Thu, 14 Jan 2016 13:52:38 +0100
From: Petr Mladek <pmladek@suse.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>, linux-kernel@vger.kernel.org,
        John Stultz <john.stultz@linaro.org>,
        Xunlei Pang <pang.xunlei@linaro.org>,
        Baolin Wang <baolin.wang@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Peter Hurley <peter@hurleysoftware.com>,
        Vasily Averin <vvs@virtuozzo.com>, Joe Perches <joe@perches.com>
Subject: Re: [PATCH 0/2] printk, Add printk.clock kernel parameter [v2]
Message-ID: <20160114125238.GU731@pathway.suse.cz>
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On Wed 2016-01-13 18:28:50, Thomas Gleixner wrote:
> You can solve the whole business by changing the timestamp in printk_log to
> 
>    u64	    mono;
>    u64	    offset_real;

This is not so easy because the structure is proceed by userspace tool,
e.g. crash, see log_buf_kexec_setup(). We would need to update all
the tools as well.


> and have a function which does:
> 
> u64 ktime_get_log_ts(u64 *offset_real)
> {
> 	*offset_real = tk_core.timekeeper.offs_real;
> 
> 	if (timekeeping_active)
> 		return ktime_get_mono_fast_ns();
> 	else
> 		return local_clock();
> }

A solution would be to apply the offset_real immediately. I wonder if
any tool expects the messages to be sorted by a monotonic clock. In
fact, it might be useful to see that some messages are disordered
against the real time, e.g. because of the leaf second.

Best Regards,
Petr