linux-kernel - Re: Excessive latency for dev

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Message-ID: <1337805903.1747.0.camel@joe2Laptop>
Date:	Wed, 23 May 2012 13:45:03 -0700
From:	Joe Perches <joe@...ches.com>
To:	Alan Stern <stern@...land.harvard.edu>, Kay Sievers <kay@...y.org>
Cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	Jason Baron <jbaron@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, Greg KH <greg@...ah.com>
Subject: Re: Excessive latency for dev_dbg?

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?


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