Excessive latency for dev_dbg?

[Alan Stern]

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?

Alan Stern

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