[PATCH v2 4/4] drm/mgag200: Use DMA to copy the framebuffer to the VRAM

[Thomas Zimmermann]

Hi

Am 15.06.23 um 19:15 schrieb Jocelyn Falempe:
> On 15/06/2023 16:24, Thomas Zimmermann wrote:
>> Hi Jocelyn
>>
>> Am 31.05.23 um 11:21 schrieb Jocelyn Falempe:
>>> Even if the transfer is not faster, it brings significant
>>> improvement in latencies and CPU usage.
>>>
>>> CPU usage drops from 100% of one core to 3% when continuously
>>> refreshing the screen.
>>
>> I tried your patchset on a HP Proliant server with a G200EH. I can see 
>> that the CPU usage goes down, but the time until the screen update 
>> reaches the hardware's video memory has increased significantly.
> 
> Thanks for taking time to test it.
> Can you check if there is something in the dmesg ?
> 
> The 1s looks suspicious, if the IRQ is not working, there is a 1s 
> timeout, which can explain why it will display only one frame per 
> second. (logs should be filled with "DMA transfer timed out")

No, I don't see that error. I also verified that the IRQ handler is 
running. It runs on each update AFAICT.

When I'm doing full-screen scrolling on the kernel console I can see the 
scanlines being updated from top to bottom. This indicates to me that 
the actual copying takes time or interferes with the scanout.

Best regards
Thomas

> 
> I will see if I can get access to a G200EH, and if I can reproduce this.
> 
> Best regards,
> 

-- 
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)
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