On Mon, Oct 26 2020 at 14:30, Marcelo Tosatti wrote:
> On Fri, Oct 23, 2020 at 11:00:52PM +0200, Thomas Gleixner wrote:
>> So without information from the driver which tells what the best number
>> of interrupts is with a reduced number of CPUs, this cutoff will cause
>> more problems than it solves. Regressions guaranteed.
>
> One might want to move from one interrupt per isolated app core
> to zero, or vice versa. It seems that "best number of interrupts
> is with reduced number of CPUs" information, is therefore in userspace,
> not in driver...
How does userspace know about the driver internals? Number of management
interrupts, optimal number of interrupts per queue?
>> Managed interrupts base their interrupt allocation and spreading on
>> information which is handed in by the individual driver and not on crude
>> assumptions. They are not imposing restrictions on the use case.
>>
>> It's perfectly fine for isolated work to save a data set to disk after
>> computation has finished and that just works with the per-cpu I/O queue
>> which is otherwise completely silent.
>
> Userspace could only change the mask of interrupts which are not
> triggered by requests from the local CPU (admin, error, mgmt, etc),
> to avoid the vector exhaustion problem.
>
> However, there is no explicit way for userspace to know that, as far as
> i know.
>
> 130: 34845 0 0 0 0 0 0 0 IR-PCI-MSI 33554433-edge nvme0q1
> 131: 0 27062 0 0 0 0 0 0 IR-PCI-MSI 33554434-edge nvme0q2
> 132: 0 0 24393 0 0 0 0 0 IR-PCI-MSI 33554435-edge nvme0q3
> 133: 0 0 0 24313 0 0 0 0 IR-PCI-MSI 33554436-edge nvme0q4
> 134: 0 0 0 0 20608 0 0 0 IR-PCI-MSI 33554437-edge nvme0q5
> 135: 0 0 0 0 0 22163 0 0 IR-PCI-MSI 33554438-edge nvme0q6
> 136: 0 0 0 0 0 0 23020 0 IR-PCI-MSI 33554439-edge nvme0q7
> 137: 0 0 0 0 0 0 0 24285 IR-PCI-MSI 33554440-edge nvme0q8
>
> Can that be retrieved from PCI-MSI information, or drivers
> have to inform this?
The driver should use a different name for the admin queues.
Thanks,
tglx
