linux-kernel - Re: [PATCH] shrink printk timestamp field

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Message-Id: <20080830101618.b6c2e1ab.akpm@linux-foundation.org>
Date:	Sat, 30 Aug 2008 10:16:18 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joe Korty <joe.korty@...r.com>
Cc:	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] shrink printk timestamp field

On Sat, 30 Aug 2008 10:38:08 -0400 Joe Korty <joe.korty@...r.com> wrote:

> On Fri, Aug 29, 2008 at 07:35:40PM -0400, Andrew Morton wrote:
> > On Wed, 27 Aug 2008 11:17:59 -0400 Joe Korty <joe.korty@...r.com> wrote:
> > 
> > > Shrink the printk timestamp field.
> > >
> > > Keep the printk timestamp from occupying more of the
> > > scarce, 80-column console line space than it really needs.
> > >
> > 
> > This is a significant loss in utility.
> > 
> > [   16.817285] md: Autodetecting RAID arrays.
> > [   16.817288] md: Scanned 0 and added 0 devices.
> > [   16.817290] md: autorun ...
> > [   16.817292] md: ... autorun DONE.
> > 
> > This not-terribly-fast machine can emit printks into the log buffer
> > within two microseconds.  That's a pretty useful ad-hoc timing
> > factility.
> > 
> > This patch will reduce the precision by a factor of five hundred.
> 
> I was looking at it from the point of view of finding out where the
> boot process was too slow.  For that millisecs is enough.  I am not
> sure where knowing printk output to the microsec would be useful for
> solving anything.
> 

Of course it's useful.  If you're working on performance or latency in
a disk, network or USB driver, microsecond resolution is about right.

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