Subject: Re: [LAU] midi triggering delay

From: andy baxter <andy@...> · Date: Wednesday, September 9, 2009 - 8:28 am

James Cameron wrote:

quoted text> On Tue, Sep 08, 2009 at 07:17:30PM -1000, david wrote:

>

>> USB not sharing interrupts with anything?

>>

>

> Andy's original post contained /proc/interrupts which showed some

> sharing was happening.  Here's a cut:

>

>  16:     380396     233180   IO-APIC-fasteoi   uhci_hcd:usb4, yenta

>  17:     829711     532117   IO-APIC-fasteoi   uhci_hcd:usb5, ohci1394, HDA Intel

>  18:          0          0   IO-APIC-fasteoi   mmc0

>  19:          2          0   IO-APIC-fasteoi   ehci_hcd:usb6

>  20:         18         17   IO-APIC-fasteoi   uhci_hcd:usb1

>  21:          0          0   IO-APIC-fasteoi   uhci_hcd:usb2

>  22:     305246     302929   IO-APIC-fasteoi   ehci_hcd:usb3

>

> Sharing interrupts adds a tiny delay to interrupt handling; if this has

> truly become significant, there's a design issue somewhere else.

>

> (Shared interrupts with modern kernels are not a huge problem, since the

> drivers check to see if the interrupt they have is legitimate before the

> kernel chains on to the next driver.  It's the waste of that additional

> check that people want to avoid.)

>

>

The usb port I'm using is on INT 21 (uhci_hcd:usb2), which doesn't share

with anything.
andy
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