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Old 10-08-08, 06:47 PM   #9
alan242
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Join Date: Sep 2006
Posts: 20
Default Re: What better, PCI-X MSI or Wired IRQ? [177.80]

Quote:
Originally Posted by logan View Post
Does this mean that only my PCIe ports support MSI?
It depends. It's been part of the PCI spec since version 2.2. I have a QStor PCI SATA card that supports MSI. You might want to do a command like
lspci -vvv |grep -E '[0-9]:[0-9][0-9]\.[0-9]|Message|Address'
and look for bridge and other devices that have the Message Signalled Interrupt capability.
I think there's also some chips on a blacklist. So you should check the boot log for any messages that indicate MSI is being disabled.

Quote:
Originally Posted by logan View Post
What if my video card is sharing with things that aren't MSI-aware/enabled? Can I still make use of EnableMSI=1?
Yes. When MSI is enabled, the kernel assigns a new IRQ number/route to the device and it is removed from the initial IRQ route. With MSI enabled, the boot log shows this as the initial IRQ when the driver is loading.

[ 7.578952] nvidia 0000:01:00.0: PCI INT A -> GSI 18 (level, low) -> IRQ 18

Then after the driver switches to MSI, /proc/interrupts looks like:

Code:
           CPU0       CPU1       
  0:    8869393        244   IO-APIC-edge      timer
  1:         13          9   IO-APIC-edge      i8042
  8:         51          1   IO-APIC-edge      rtc0
  9:          0          4   IO-APIC-fasteoi   acpi
 14:          0          0   IO-APIC-edge      pata_atiixp
 15:          0          0   IO-APIC-edge      pata_atiixp
 16:     104814          1   IO-APIC-fasteoi   ohci_hcd:usb1, HDA Intel
 17:          1          1   IO-APIC-fasteoi   ohci_hcd:usb2, ohci_hcd:usb4
 18:          1          1   IO-APIC-fasteoi   ohci_hcd:usb3, ohci_hcd:usb5
 21:          2          1   IO-APIC-fasteoi   ohci1394
 22:     530004         28   IO-APIC-fasteoi   ahci, ohci_hcd:usb6
218:        291      74047   PCI-MSI-edge      nvidia
219:       1339     566655   PCI-MSI-edge      eth0
220:          0          4   PCI-MSI-edge      sata_qstor
221:       1272     253824   PCI-MSI-edge      ehci_hcd:usb7
Quote:
Originally Posted by logan View Post
I see that ajw1980 just posted about problems resuming with EnableMSI=1. Is anyone else using this? How's it so far?
YMMV.

On one system I have (AMD 770 / 7600GS), it works quite well.

On a another system I have (MCP51 / 6150PV), it works but Bad Things(TM) under heavy load. I haven't had time to figure out what's up with that one yet as it's a MythTV box as most of the IRQs are unshared and the box is usually busy.

Alan
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