Query about "Function call interrupts" entry in /proc/interrupts file

[iamrivu]

Hi all,

In the /proc/interrupts file, there is one entry called "Function
call interrupts".
Can anyone please explain to me how this interrupt is generated or
what it does?
Thanks!

--Agniv

$ cat /proc/interrupts

CPU0 CPU1
0: 7555 0 IO-APIC-edge timer
1: 2 0 IO-APIC-edge i8042
4: 2 0 IO-APIC-edge
6: 5 0 IO-APIC-edge floppy
7: 0 0 IO-APIC-edge parport0
8: 1 0 IO-APIC-edge rtc0
9: 0 0 IO-APIC-fasteoi acpi
12: 4 0 IO-APIC-edge i8042
14: 5184503 0 IO-APIC-edge ata_piix
15: 0 0 IO-APIC-edge ata_piix
16: 10030496 0 IO-APIC-fasteoi ohci1394, HDA Intel
17: 33961000 0 IO-APIC-fasteoi eth0
18: 0 0 IO-APIC-fasteoi uhci_hcd:usb4
21: 2710967 0 IO-APIC-fasteoi ehci_hcd:usb1, uhci_hcd:usb2
22: 0 0 IO-APIC-fasteoi uhci_hcd:usb3
23: 0 0 IO-APIC-fasteoi uhci_hcd:usb5
2299: 2594538 0 PCI-MSI-edge ahci
NMI: 0 0 Non-maskable interrupts
LOC: 175008553 173744798 Local timer interrupts
RES: 1503295 3085980 Rescheduling interrupts
CAL: 1361 2486 Function call interrupts
TLB: 546223 608398 TLB shootdowns
SPU: 0 0 Spurious interrupts
ERR: 0
MIS: 0

[Rubberman]

Man, this is being pulled out of my deep, dark past! Anyway, system functions are normally executed with a software interrupt. DOS system call interrupts were IRQ10 as I recall. To execute a system function, you would assign the arguments to some system registers (or push them onto the stack, which I don't recall exactly as I haven't done any of this for about 20 years) and then issue the interrupt. The INT10 system handler would look at the registers and/or stack and call the appropriate function. This is how the bios bootstraps the operating system. In fact, the last time I really got into this stuff was in the mid-80's when I was writing boot loaders.

[iamrivu]

Rubberman,
Thanks a lot for replying to my question!
I have been pretty late in thanking you and I apologize for that.
From your reply what I understood is function call interrupts actually count software interrupts, executed by the INT <> instruction.
However, I found out that this is not the case.
I've used one small assembly instruction in which I use the INT 0x80 instruction a number of times in a loop. This hasn't led to a single change in the number of function call interrupts. So the function call interrupts do not count the software interrupts at all.
Please correct me if I'm wrong.
Thanks once again.