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Date: Fri, 28 Apr 2017 10:35:32 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Petr Mladek <pmladek@suse.com>,
 Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
 Andrew Morton <akpm@linux-foundation.org>,
 Peter Zijlstra <peterz@infradead.org>,
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 Martin Schwidefsky <schwidefsky@de.ibm.com>,
 David Miller <davem@davemloft.net>
Subject: Re: [PATCH v5 1/4] printk/nmi: generic solution for safe printk in NMI
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On (04/27/17 12:14), Steven Rostedt wrote:
[..]
> I tried this patch. It's better because I get the end of the trace, but
> I do lose the beginning of it:
> 
> ** 196358 printk messages dropped ** [  102.321182]     perf-5981    0.... 12983650us : d_path <-seq_path

many thanks!

so we now drop messages from logbuf, not from per-CPU buffers. that
"queue printk_deferred irq_work on every online CPU when we bypass per-CPU
buffers from NMI" idea *probably* might help here - we need someone to emit
messages from the logbuf while we printk from NMI. there is still a
possibility that we can drop messages, though, since log_store() from NMI
CPU can be much-much faster than call_console_drivers() on other CPU.

	-ss