Interrupt Descriptions

[John Baldwin]

On Thursday 01 October 2009 8:49:43 am Andriy Gapon wrote:
> on 01/10/2009 00:32 John Baldwin said the following:
> > A few folks have asked recently for the ability to add descriptive strings to 
> > registered interrupt handlers.  This is especially true since the advent of 
> > MSI with multiple interrupts per device.  I hacked up a prototype today that 
> > adds a new 'bus_describe_intr()' that takes the IRQ resource, the void * 
> > cookie returned by bus_setup_intr() and var args description and appends that 
> > to the interrupt name in the thread and vmstat -i info.  The current patch 
> > only has the MI bits and the MD bits for amd64 as well as a sample change to 
> > the igb(4) driver.
> > 
> > The patch is at http://www.FreeBSD.org/~jhb/patches/intr_describe.patch.
> > 
> > An example from this patch is:
> > 
> >> vmstat -i
> > interrupt                          total       rate
> > irq1: atkbd0                           8          0
> > irq4: uart0                          751          5
> > irq6: fdc0                             6          0
> > irq14: ata0                           36          0
> > irq20: uhci0                          20          0
> > irq23: uhci3 ehci0                     2          0
> > irq28: mpt0                         1661         11
> > irq256: igb0:tx 0                    880          6
> > irq257: igb0:rx 0                   1098          7
> > irq258: igb0:link                      3          0
> > irq259: igb1:tx 0                      1          0
> > irq260: igb1:rx 0                    134          0
> > irq261: igb1:link                      3          0
> > 
> 
> Example above doesn't demonstrate what happens when there are shared interrupts.
> Would it still look nice (with sufficiently long descriptions)?

Currently MSI interrupts generally aren't shared.  If they are shared what
happens is that the 'name:descr' bit is treated as the full name of the
device and the normal "+" or "*" truncation stuff kicks in so you would
maybe have:

irq280: igb0:tx 0 igb0:tx 1

except that doesn't fit in MAXCOMLEN so you would have:

irq280: igb0:tx 0+

For the ithread name we are stuck with MAXCOMLEN.  I would like to overhaul
the intrcnt stuff to possibly allow for longer names and be mostly MI (having
all the longs shared across cache lines that might be shared by multiple CPUs
isn't ideal either at this point).  I am considering having either an array or
list of intrcnt structures with a name and a count with a sysctl that exports
an array for vmstat to use (the kvm bits could always rebuild the list using
the same logic as the sysctl handler for crash dumps).  The current design is
very limiting and forces the weird space padding to make renaming intrcnt
descriptions manageable when adding/removing interrupt handlers.

-- 
John Baldwin