Re: kern/56857: ixg(4) doesn't work in legacy interrupt mode

[Masanobu SAITOH <msaitoh%execsw.org@localhost>]

On 2022/05/29 2:00, Manuel Bouyer wrote:
> The following reply was made to PR kern/56857; it has been noted by GNATS.
> 
> From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
> To: gnats-bugs%netbsd.org@localhost
> Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
> Subject: Re: kern/56857: ixg(4) doesn't work in legacy interrupt mode
> Date: Sat, 28 May 2022 18:58:48 +0200
> 
>  On Thu, May 26, 2022 at 11:35:01AM +0000, bouyer%antioche.eu.org@localhost wrote:
>  >  [...]
>  > 
>  > 	cause igx(4) device to fail to receive packet (or to receive them
>  > 	with very high latency). Other devices, including nvme(4) and wm(4)
>  > 	works fine in legacy mode. This is a show stopper for Xen (see PR
>  > 	kern/55667).
>  > 	The device works fine with MSI-X. I coulnd't test with MSI as
>  > 	disabling only MSI-X cause the kernel to panic (probably unrelated to
>  > 	igx(4)), but experiments with Xen suggest that it fails too.
>  
>  Restricting the Xen dom0 to a single CPU makes ixg work with MSI.
>  So maybe the issue is that too much queues are allocated when one interrupt
>  per queue is not available ?
>  
>  -- 
>  Manuel Bouyer <bouyer%antioche.eu.org@localhost>
>       NetBSD: 26 ans d'experience feront toujours la difference
>  --

I think I could reproduce the same problem with amd64/conf/GENERIC + your test patch.
(i.e. not dom0).

An event counter of ixgbe:

	ixg0 MAC Statistics Interrupt conditions zero          30    0 misc

ixgbe_legacy_irq() increment the counter for each receiving packet and
return quickly.

-- 
-----------------------------------------------
                SAITOH Masanobu (msaitoh%execsw.org@localhost
                                 msaitoh%netbsd.org@localhost)