Interrupt Descriptions

[Bruce Evans]

On Thu, 1 Oct 2009, John Baldwin wrote:

> On Wednesday 30 September 2009 8:02:57 pm Bruce Evans wrote:
>> On Wed, 30 Sep 2009, John Baldwin wrote:
>>
>>> 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
>>
>> Interrupt names should be no longer than 4 (5 works sometimes) characters so
>> that they can be displayed by systat -v.
>
> For the machines this is targeted at (i.e. ones with devices using MSI/MSI-X)
> the number of interrupts is already well beyond what systat -v can currently
> display anyway.

This should be fixed before expanding the names into descriptions.

I wonder what uses all these interrupts.  Most FreeBSD cluster machines use
a whole 3 interrupts apart from acpi_timer, with 1 barely active (1 disk,
1 net, and 1 serial i/o probably only used for a serial console).  My
workstations use about 10 plus timers, but most are usually inactive
except for net, keyboard and sometimes disk.  Does anyone have systems
more than about 16 disk controllers and 16 network cards so as to need
more than 32 interrupts?

> I believe most folks use vmstat -i or ithread stats in top
> to measure real-time interrupts at this point.  Possibly systat could grow a
> new interrupt-only mode that has sufficient room for full interrupt names.

I don't find static info and thus vmstat -i very useful.  vmstat with a
repeat interval is useful, but for some reason vmstat -i never supported
the repeat interval (its multi-line display is certainly unsuitable for
repetitions being readable), and with systat -v repetition in vmstat -i
is rarely missed.  A repeating vmstat -i would have even more space
problems than systat -v, since it would want to repeat single line output.

systat and most things just want a unique tag, not a description or even
a full name.  The full name could be looked up from a tag by looking at
vmstat -i output which could show both.

>
> FYI, it actually looks decent enough running a 7.x systat on a test 9.0 kernel:
>
>                                     25000 frevn          pdpgs  2000 cpu0: time
>                                                          intrn       igb0:tx 0
> Disks   da0 pass0                                  473896 wire     25 igb0:rx 0
> KB/t   0.00  0.00                                   13872 act         igb0:link
> tps       0     0                                   10080 inact       igb1:tx 0
> MB/s   0.00  0.00                                     128 cache     1 igb1:rx 0
> %busy     0     0                                 7603460 free        igb1:link
>
> For these devices with MSI, the description (tx 0, tx 1, link, etc.) is
> actually more meaningful than the IRQ.

The irq is probably least useful for most devices.

The above is only reasonable because I changed systat to move "irqN:
" to " irqN" at the end.  "irq256: bce0" on FreeBSD cluster machines
is displayed reasonably as "bce0 256".  But systat shouldn't have to
do this.  At least the form of the names used by systat (== the one
given by the old intrnames API) should have names that are carefully
phrased to have the most useful info first, and to not waste space
with ": " or even "irq".

Bruce