linux-kernel - Re: early_printk accessing __log

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Message-Id: <200707231815.38124.rgetz@blackfin.uclinux.org>
Date:	Mon, 23 Jul 2007 18:15:37 -0400
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Mike Frysinger" <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org, "Greg Ungerer" <gerg@...pgear.com>,
	"Russell King" <rmk@....linux.org.uk>,
	"Paul Mundt" <lethal@...ux-sh.org>,
	"Tim Bird" <tim.bird@...sony.com>, bryan.wu@...log.com
Subject: Re: early_printk accessing __log_buf

On Mon 23 Jul 2007 16:15, Andrew Morton pondered:
> This code would be
> simpler if it did not attempt to read more than one char at a time.  It
> will be plenty fast enough.

When systems have NMI kick off due to power failure, and you want to grab the 
log buffer to write it to flash before power really dies - every cycle 
counts.

A single function which does the copy as a loop (existing) is going to be much 
faster than the overhead of 1024 function calls to copy the last k.

> The magical interpretation of len isn't very nice. 

There are lots of places in the kernel which have magic in them :)

-Robin
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