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Date: Wed, 15 Nov 2017 09:48:38 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Mark Salyzyn <salyzyn@android.com>
Cc: Petr Mladek <pmladek@suse.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Prarit Bhargava <prarit@redhat.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [GIT pull] printk updates for 4.15
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Hello Mark,

On (11/14/17 07:56), Mark Salyzyn wrote:
[..]
> Thanks for the vote of confidence :-) but we were holding back re spinning
> that set until the ability to switch the primary timestamp got accepted. (we
> were to use U suffix for realtime, B for boottime etc to designate them).
> 
> Printing the other timebases during major disruptions (suspend/resume/etc)
> was needed for our battery monitoring analysis tools, and we only used them
> as synchronization markers as a secondary effect.
> 
> But we _also_ had Android partners asking if it was possible to switch the
> primary (dmesg) timestamp to one of boottime or realtime to aid in triaging
> temporal issues. Doing so in the tool was sometimes too inaccurate
> (~+/-20ms) even with help sniffing the periodic synchronization/disruption
> prints. Switching the timebase for dmesg gave us roughly 1000 times more
> comparative time precision which helps immensely when trying to correlate
> and order the sequence of events in user space and kernel activities.

have you considered trace points?

	-ss