lkml.org 
[lkml]   [2008]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: Should irq_chip->mask disable percpu interrupts to all cpus, or just to this cpu?
Ingo Molnar <mingo@elte.hu> writes:

> * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
>> Hi,
>>
>> I'm reworking Xen's interrupt handling to isolate it a bit from the
>> workings of the apic-based code, as Eric suggested a while back.
>>
>> As I've mentioned before, Xen represents interrupts as event channels.
>> There are two major classes of event channels: per-cpu and, erm, not
>> percpu. Per-cpu event channels are for things like timers and IPI
>> function calls which are inherently per-cpu; it's meaningless to
>> consider, for example, migrating them from cpu to cpu. I guess
>> they're analogous to the the local apic vectors.
>>
>> (Non-percpu event channels can be bound to a particular cpu, and
>> rebound at will; I'm not worried about them here.)
>>
>> Previously I allocated an irq per percpu event channel per cpu. This
>> was pretty wasteful, since I need about 5-6 of them per cpu, so the
>> number of interrupts increases quite quickly as cpus does. There's no
>> deep problem with that, but it gets fairly ugly in /proc/interrupts,
>> and there's some tricky corners to manage in suspend/resume.

Every high performance device wants one irq per cpu.
So if it gets ugly in /proc/interrupts we should look at fixing
/proc/interrupts.

It looked like in Xen each of those interrupts were delivered
to different event channels. Did I misread that code?

I really hate the notion of sharing a single irq_desc across
multiple cpus as a preferred mode of operation. As NUMA comes
into play it guarantees we will have cross cpu memory fetches
on a fast path for irq handling.

Other than the beautiful way we print things in /proc/interrupts
IRQ_PER_CPU feels like a really bad idea. Especially in that
it enshrines the nasty per cpu irq counters that scale horribly.

Eric


\
 
 \ /
  Last update: 2008-09-24 12:09    [W:0.110 / U:0.528 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site