linux-kernel - Re: serial flow control appears broken

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Date:	Mon, 30 Jul 2007 10:45:19 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Russell King <rmk+lkml@....linux.org.uk>
cc:	Robert Hancock <hancockr@...w.ca>,
	Lee Howard <faxguy@...ardsilvan.com>,
	linux-serial@...r.kernel.org, tytso@....edu,
	linux-kernel@...r.kernel.org
Subject: Re: serial flow control appears broken

On Sat, 28 Jul 2007, Russell King wrote:

> Essentially, any complex interrupt handler (such as an IDE interrupt
> doing a multi-sector PIO transfer _in interrupt context_) can cause this
> kind of starvation.  That's why Linux 1.x had bottom halves - so that
> the time consuming work could be moved out of the interrupt handler,
> thereby causing minimal the blockage of other interrupts.
> 
> Unfortunately, that kind of design has been long since forgotten.
> Apparantly modern machines are fast enough that it doesn't have to be
> worried about anymore...  Or are they?

 I would guess it is not that the machines are fast enough, but that this 
two-level processing makes things more complicated.  Enough that most 
people would not bother digging into it unless really forced.  Only 
occasional latency problems are probably not enough of a force.

  Maciej
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