Re: a joint letter on low latency and Linux

[Theodore Y. Ts'o]

   From: Benno Senoner <[e-mail]>
   Date: 	Fri, 30 Jun 2000 04:16:14 +0200

   assume someone rolls out a clean low latency approach for 2.4 ,
   would you accept the patches or would you delay the stuff to 2.5 ?
   (I have no idea if it is a big amount of work)

I'd like to remind people that we're at Linux 2.4.0test2, and **test**,
plus Linus's earlier declaration of a code (really feature) freeze imples
this is probably not the time to be making changes to core kernel
internals?   

I'd really like a stable Linux kernel released sometime before the end
of this century, thank you very much.

   Date: 	Thu, 29 Jun 2000 20:02:02 -0700 (PDT)
   From: Linus Torvalds <[e-mail]>

   More than just numbers, but yes. I'd like to know that the code isn't just
   crap. For example, let's say that something uses an O(n^3) algorithm, and
   to "overcome" the expense of this thing we add scheduling points in it.
   That's the easy way to do it. But maybe the right thing to do is to
   realize that the code may be badly structured in the first place?

Ah, you've looked at the POSIX byte-range locking code recently, have
you?  The last time Al Viro, Ben LaHaise, and I looked at it, we think
we figured out that it was O(n^3), but having just eaten, we didn't
spend more time looking at it than was necessary.  :-)

   From: David Schleef <[e-mail]>
   Date: 	Fri, 30 Jun 2000 04:06:29 -0700

   How about these?

     - Winmodems

For $30 dollars, you can buy yourself a real modem.  (And be much happier)

(We don't have any real drivers for them anyway; well, there are two GPL
violations, which I need work on....)

     - crappy UARTs running at high speeds

For $10 dollars, you can buy yourself a real UART.  (And be much happier)

     - High-accuracy stratum-1 NTP servers
     - Almost any data acquisition application with a board that
       costs less than USD 1000.

And these are common applications?  More importantly, both are ones
which can *easily* be handled by RT Linux.

Multimedia applications are the only ones people have listed that for
which I'm even remotely sympathetic, and there I agree that 100-300ms
latency in the kernel is bad, and we need to get that down.  But please,
make that a 2.5 priority.  

(I'll note that on my SMP machine, I'm running MP3 decoders much of the
time, and in practice very rarely hear any dropouts.  So the folks who
are painting such a dire picture of the state of Multimedia are
overstating their case a little, I think.)

							- Ted