Re: [PATCH] xen/netfront: Fix TX response spurious interrupts

["Anthoine Bourgeois" <anthoine.bourgeois@xxxxxxxxxx>]

On Thu, Jul 10, 2025 at 01:05:47PM -0700, Elliott Mitchell wrote:
>On Thu, Jul 10, 2025 at 04:11:15PM +0000, Anthoine Bourgeois wrote:
>> We found at Vates that there are lot of spurious interrupts when
>> benchmarking the PV drivers of Xen. This issue appeared with a patch
>> that addresses security issue XSA-391 (see Fixes below). On an iperf
>> benchmark, spurious interrupts can represent up to 50% of the
>> interrupts.
>
>If this is the correct fix, near-identical fixes are needed for *all*
>of the Xen front-ends.  Xen virtual block-devices and Xen PCI-passthrough
>devices are also effected by a similar issue.
>
blkfront doesn't call the response handle from multiple places. It
doesn't seem to be affected by this problem.
And pcifront neither.

>Thanks for finding a candidate fix, this effects many other people who
>have been troubled by this performance issue.
>
>FreeBSD will also need a similar fix.

In FreeBSD, netfront may also be affected.
xn_assemble_tx_request calls xn_txeof.
blkfront and pcifront seems good.

Regards,
Anthoine


Anthoine Bourgeois | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech