linux-kernel - Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings

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Date:	Thu, 21 Jan 2016 11:08:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, rafael@...nel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	nicolas.pitre@...aro.org, vincent.guittot@...aro.org
Subject: Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings

On Thu, Jan 21, 2016 at 10:50:27AM +0100, Daniel Lezcano wrote:

> Actually, the handle passes dev_id in order to let the irqtimings to sort
> out a shared interrupt and prevent double sampling. In other words, for
> shared interrupts, statistics should be per t-uple(irq , dev_id) but that is
> something I did not implemented ATM.
> 
> IMO, the handler is at the right place. The prediction code does not take
> care of the shared interrupts yet.

That certainly added to the confusion. But if you want per dev_id stats,
the whole alloc framework is 'broken' too, for it allocates the stuff
per irq.

> I tried to find a platform with shared interrupts in the ones I have
> available around me but I did not find any. Are the shared interrupts
> something used nowadays or coming from legacy hardware ? What is the
> priority to handle the shared interrupts in the prediction code ?

They're less common (thankfully) than they used to be, but I still have
them:

root@...-ep:~# cat /proc/interrupts | grep ","
  59:          0          0          0          0          0          0
  0          0          0          0          0          0          0
  0          0          0          0          0          0          0
  0          0          0          0          0          0          0
  0          0          0          0          0          0          0
  0          0          0          0          0          0   IO-APIC
  5-fasteoi   i801_smbus, i801_smbus

root@...-ep:~# cat /proc/interrupts | grep ","
 18:          0          0          0          0          0          0          0          0          0          0          0          0   IO-APIC  18-fasteoi   ehci_hcd:usb1, uhci_hcd:usb6
 19:    9695230   19577242   13205011    3970578     740376    1138693          0          0          0          0          0          0   IO-APIC  19-fasteoi   uhci_hcd:usb5, ata_piix
 23:          3          0          0          0        927          0          0          0          0          0          0          0   IO-APIC  23-fasteoi   ehci_hcd:usb2, uhci_hcd:usb4

root@snb:~# cat /proc/interrupts | grep ","
 19:   11058485          0          0          0          0          0          0          0   IO-APIC  19-fasteoi   ata_piix, ata_piix


Also there's a whole host of SOCs that has them.