RE: Updated MSI Patches

Nguyen, Tom L
2003-08-13T15:19:13Z

>> Salability means many things. I'm not sure which aspect you are talking
>> about, but a good thing with MSI is that it does not depend on I/O
>> APICs. A typical I/O APIC has 24 RTEs, and we need about 10 I/O APICs to
>> consume the vectors.

> Yes there are already a number of systems which exhibit this problem (see
> the URL in the next comment)

>> You can make this scale on SMP systems. The vector-based approach would
>> be easier to extend it per-CPU because vectors are inherently per-CPU,
>> compared with IRQ-based. Today we have IRQ balancing as you know, and
>> the key part is to bind IRQ to a particular CPU (BTW, with our patch it
>> happens automatically because the balancer does not care if they are IRQ
>> or vector).

>Sorry, yeah i meant device scalability essentially, the ability to plug in
>a fair amount of these and other devices into the same system. The per cpu
>IDT route is also worthwhile following a bit later on. I've already
>written something along the lines of a per node IDT (you could make the
>granularity per cpu of course) if you're interested you can have a look
>here http://www.osdl.org/projects/numaqhwspprt/results/patch-numaq-highirq10 it
>also has a companion patch to dynamically allocate the irq_desc's which
>applies on top of it http://function.linuxpower.ca/patches/patch-dynirq-wli

>But back to the subject, your patch looks good, i'll test it for
>regression (no MSI devices but regression testing is just as important)
>when you next post.
I already had discussion with Jun about this change. We will post it as soon as
we validate this change on our system.

Thanks,
Long