linux-kernel - Re: Excessive latency for dev

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Message-ID: <20120524021208.GA12557@kroah.com>
Date:	Wed, 23 May 2012 19:12:08 -0700
From:	Greg KH <greg@...ah.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Alan Stern <stern@...land.harvard.edu>, Kay Sievers <kay@...y.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Jason Baron <jbaron@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Excessive latency for dev_dbg?

On Wed, May 23, 2012 at 01:45:03PM -0700, Joe Perches wrote:
> cc'ing Kay.
> 
> On Wed, 2012-05-23 at 16:37 -0400, Alan Stern wrote:
> > I just tried doing some testing of 3.4.  Sequences of literally
> > adjacent dev_dbg() calls -- with local interrupts disabled -- show up
> > in the log buffer spaced at time intervals between 1 and 4
> > milliseconds!
> > 
> > This is with CONFIG_DYNAMIC_DEBUG not enabled, and CONFIG_PRINTK_TIME,
> > CONFIG_PREEMPT, CONFIG_HIGH_RES_TIMERS, and CONFIG_HPET_TIMER all set
> > to y.
> > 
> > What's going on here?  Did printk suddenly slow down a lot?  Or has the
> > timer code gone crazy?

Joe, why ask Kay?  He didn't touch this code until 3.5-rc1, and Alan is
testing 3.4.

confused,

greg k-h
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