On 2014/8/1 21:16, Arnd Bergmann wrote:
> On Wednesday 30 July 2014, Yijing Wang wrote:
>>>>>
>>>>> The other part I'm not completely sure about is how you want to
>>>>> have MSIs map into normal IRQ descriptors. At the moment, all
>>>>> MSI users are based on IRQ numbers, but this has known scalability problems.
>>>>
>>>> Hmmm, I still use the IRQ number to map the MSIs to IRQ description.
>>>> I'm sorry, I don't understand you meaning.
>>>> What are the scalability problems you mentioned ?
>>> We have soft limitation of nr_irqs or hard limitation NR_IRQS,
>>> we couldn't allocate as much irq number as we need in some cases,
>>> such as to support MSI-x.
>>
>> Oh, yes, this is a potential issue. Gerry, thanks for you explanation. :)
>
> This should no longer be an issue, as arm64 uses CONFIG_SPARSE_IRQ
> and the number of interrupts is not limited in any form.
>
> My point was more that the device driver should not need to care about
> the interrupt number: it gets made up on the spot when the MSI is
> needed, and then it is only used to request the IRQ. This can be
> simplified into one interface at the device driver level, even though
> the internal still use numbers somewhere. If we ever remove IRQ numbers
> from the driver API, this part doesn't need to get touched again.
>
Hi Arnd, I have another question is some drivers will request more than one
MSI/MSI-X IRQ, and the driver will use them to process different things.
Eg. network driver generally uses one of them to process trivial network thins,
and others to transmit/receive data.
So, in this case, it seems to driver need to touch the IRQ numbers.
wr-linux:~ # cat /proc/interrupts
CPU0 CPU1 CPU2 .... CPU17 CPU18 CPU19 CPU20 CPU21 CPU22 CPU23
......
100: 0 0 0 0 0 0 0 0 0 0 IR-PCI-MSI-edge eth0
101: 2 0 0 0 0 0 302830488 0 0 0 IR-PCI-MSI-edge eth0-TxRx-0
102: 110 0 0 0 0 360675897 0 0 0 0 IR-PCI-MSI-edge eth0-TxRx-1
103: 109 0 0 0 0 0 0 0 0 0 IR-PCI-MSI-edge eth0-TxRx-2
104: 107 0 0 9678933 0 0 0 0 0 0 IR-PCI-MSI-edge eth0-TxRx-3
105: 107 0 0 0 357838258 0 0 0 0 0 IR-PCI-MSI-edge eth0-TxRx-4
106: 115 0 0 0 0 0 0 0 0 0 IR-PCI-MSI-edge eth0-TxRx-5
107: 114 0 0 0 0 0 0 337866096 0 0 IR-PCI-MSI-edge eth0-TxRx-6
108: 373801199 0 0 0 0 0 0 0 0 0 IR-PCI-MSI-edge eth0-TxRx-7
Thanks!
Yijing.
>
> .
>
--
Thanks!
Yijing
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