Hi

Am 04.06.25 um 23:43 schrieb Michael Kelley:
[...]

Nonetheless, there's an underlying issue. A main cause of the difference
is the number of messages to Hyper-V to update dirty regions. With
hyperv_fb using deferred I/O, the messages are limited 20/second, so
the total number of messages to Hyper-V is about 480. But hyperv_drm
appears to send 3 messages to Hyper-V for each line of output, or a total of
about 3,000,000 messages (~90K/second). That's a lot of additional load
on the Hyper-V host, and it adds the 10 seconds of additional elapsed
time seen in the guest. There also this ugly output in dmesg because the
ring buffer for sending messages to the Hyper-V host gets full -- Hyper-V
doesn't always keep up, at least not on my local laptop where I'm
testing:

[12574.327615] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12574.327684] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12574.327760] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12574.327841] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12597.016128] hyperv_sendpacket: 6211 callbacks suppressed
[12597.016133] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12597.016172] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12597.016220] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11
[12597.016267] hyperv_drm 5620e0c7-8062-4dce-aeb7-520c7ef76171: [drm] *ERROR* Unable to send packet via vmbus; error -11

hyperv_drm could be fixed to not output the ugly messages, but there's
still the underlying issue of overrunning the ring buffer, and excessively
hammering on the host. If we could get hyperv_drm doing deferred I/O, I
would feel much better about going full-on with deprecating hyperv_fb.

I try to address the problem with the patches at

https://lore.kernel.org/dri-devel/20250605152637.98493-1-tzimmermann@suse.de/ (local)

Testing and feedback is much appreciated.

Best regards
Thomas

Michael

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)