Hi, I was going thru the LDD 3 and stumbled upon this. There is an instance while explaining spin_lock_bh() function that the author mentions that this only disables the "Software Interrupts"( LDD 3,page number 119). In the immediately next paragraph, these "Software Interrupts" are linked to "tasklets". I am not able to fully understand this point. It would be really nice if some one elaborated on this. Regards, Aravind. "Dovie'andi se tovya sagain" -Mat Cauthon (WoT). -----Original Message----- From: Alistair Reay [mailto:Alistair.Reay@xxxxxxxxxx] Sent: Thursday, October 25, 2007 2:06 AM To: Thippeswamy, Aravind; kernelnewbies@xxxxxxxxxxxx Subject: RE: IPX performance 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). -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ ========================================================== For more information on the Television New Zealand Group, visit us online at tvnz.co.nz ========================================================== CAUTION: This e-mail and any attachment(s) contain information that is intended to be read only by the named recipient(s). This information is not to be used or stored by any other person and/or organisation. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
