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

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

The following reply was made to PR kern/56857; it has been noted by GNATS.

From: Masanobu SAITOH <msaitoh%execsw.org@localhost>
To: gnats-bugs%netbsd.org@localhost, msaitoh%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 netbsd-bugs%netbsd.org@localhost, bouyer%antioche.eu.org@localhost
Cc: msaitoh%execsw.org@localhost
Subject: Re: kern/56857: ixg(4) doesn't work in legacy interrupt mode
Date: Sun, 29 May 2022 13:43:10 +0900

 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)