RE: IPX performance

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Hi Aravind,
It pays to be precise when talking about these terms. "Software
Interrupt" is a bit of a misnomer because software never really
interrupts a cpu, it does not alter the sequence of instructions. Maybe
what you mean is; what is the difference between and interrupt and an
exception?

Interrupts are only raised by hardware devices such as interval timers
and I/O devices like the keyboard or network card. A hardware circuit
called the Interrupt Controller waits for a hardware event and when one
occurs interrupts the kernel. It is then the kernel's job to service the
interrupt with the appropriate handler. This may mean eventually waking
up a user process to deal with the data (ie. Wake up httpd to deal with
new network data for tcp/80).

Exceptions are raised by the cpu when executing instructions in either
user or kernel mode. A programming error, like trying to divide a number
by zero, will raise an exception and the kernel will signal the process
(in this case with a SIGFPE) and then request that the program handle
the error, or failing that, abort the process. Exceptions aren't all
about bad news though, a process will always cause plenty of exceptions
when it first starts up as it tries to access memory pages that haven't
been allocated by the kernel yet.

There is a type of exception called a "Programmed Exception" which is
used to implement system calls and set debugging information, I have
heard of this being called a "software interrupt". Maybe this is what
you want to know?

Hope this helps!

Cheers
Al

-----Original Message-----
From: kernelnewbies-bounce@xxxxxxxxxxxx
[mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of Thippeswamy,
Aravind
Sent: Thursday, 25 October 2007 3:51 a.m.
To: kernelnewbies@xxxxxxxxxxxx
Subject: RE: IPX performance

Hi,
	Can any one kindly tell me what "Software Interrupt" exactly
means? Also, how is it different from the "Hardware Interrupt"?

Regards,
Aravind.
 
"Dovie'andi se tovya sagain"
 -Mat Cauthon (WoT).

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