amrd disk performance drop after running under high load

[Scott Long]

Boris Samorodov wrote:
> Hi!
> 
> Since nobody answered so far, here is my two cents. I'm not an expert
> here so it's only my imho.
> 
> On Wed, 17 Oct 2007 22:52:49 +0400 Alexey Popov wrote:
> 
>> interrupt                          total       rate
>> irq6: fdc0                             8          0
>> irq14: ata0                           47          0
>> irq16: uhci0                  1428187319       1851
>                                 ^^^^^^^^^^       ^^^^ [1]
>> irq18: uhci2                    12374352         16
>> irq23: ehci0                           3          0
>> irq46: amr0                     11983237         15
>> irq64: em0                    1427141755       1850
>                                 ^^^^^^^^^^       ^^^^ [2]
>> cpu0: timer                   1540896452       1997
>> cpu1: timer                   1542377798       1999
>> Total                         5962960971       7730
> 
> [1] and [2] looks suspicious to me (totals and rate are too close to
> each other and btw to timers). Let the latter (timers) alone. Do you
> use any USB device? Can you try to use other network card? That
> behaviour seems to be an interrupt storm and/or irq collision.
> 
> 

It's neither.  It's a side effect of a feature that FreeBSD abuses for
handling interrupts.  Note that amr0 and ehci2 are acting similar.  It's
mostly harmless, but it does waste CPU cycles.  I wouldn't expect this
on a recent version of FreeBSD, though, at least not from the e1000
driver.

Scott