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

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

On Tue, Jul 15, 2025 at 12:19:34PM -0700, Elliott Mitchell wrote:
>On Tue, Jul 15, 2025 at 08:21:40AM +0000, Anthoine Bourgeois wrote:
>> On Mon, Jul 14, 2025 at 05:37:51PM -0700, Elliott Mitchell wrote:
>> >On Mon, Jul 14, 2025 at 07:11:06AM +0000, Anthoine Bourgeois wrote:
>> >> On Fri, Jul 11, 2025 at 05:33:43PM +0200, Juergen Gross wrote:
>> >> >On 10.07.25 18:11, Anthoine Bourgeois wrote:
>> >
>> >Tested on a VM which this could be tried on.
>> >
>> >Booting was successful, network appeared to function as it had been.
>> >Spurious events continued to occur at roughly the same interval they had
>> >been.
>> >
>> >I can well believe this increases Xen network performance and may
>> >reduce the occurrence of spurious interrupts, but it certainly doesn't
>> >fully fix the problem(s).  Appears you're going to need to keep digging.
>> >
>> >I believe this does count as Tested-by since I observed no new ill
>> >effects.  Just the existing ill effects aren't fully solved.
>> >
>>
>> Thank you for the test!
>> Could you send me the domU/dom0 kernel version and xen version ?
>
>I tend to follow Debian, so kernel 6.1.140 and 4.17.6.  What may be
>more notable is AMD processor.
>
>When initially reported, it was reported as being more severe on systems
>with AMD processors.  I've been wondering about the reason(s) behind
>that.

AMD processors could make a huge difference. On Ryzen, this patch could
almost double the bandwidth and on Epyc close to nothing with low
frequency models, there is another bottleneck here I guess.
On which one do you test?

Do you know there is also a workaround on AMD processors about remapping
grant tables as WriteBack?
Upstream patch is 22650d605462 from XenServer.
The test package for XCP-ng with the patch:
https://xcp-ng.org/forum/topic/10943/network-traffic-performance-on-amd-processors

Regards,
Anthoine


Anthoine Bourgeois | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

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