Nouveau - Aug 2019 - DMA-API: cacheline tracking ENOMEM, dma-debug disabled due to nouveau ?

Hello

Since lot of release (at least since 4.19), I hit the following error message:
DMA-API: cacheline tracking ENOMEM, dma-debug disabled

After hitting that, I try to check who is creating so many DMA mapping and see:
cat /sys/kernel/debug/dma-api/dump | cut -d' ' -f2 | sort | uniq -c
      6 ahci
    257 e1000e
      6 ehci-pci
   5891 nouveau
     24 uhci_hcd

Does nouveau having this high number of DMA mapping is normal ?

Regards

On Wed, Aug 14, 2019 at 04:50:33PM +0200, Corentin Labbe
wrote:
> Hello
> 
> Since lot of release (at least since 4.19), I hit the following error
message:
> DMA-API: cacheline tracking ENOMEM, dma-debug disabled
> 
> After hitting that, I try to check who is creating so many DMA mapping and
see:
> cat /sys/kernel/debug/dma-api/dump | cut -d' ' -f2 | sort | uniq -c
>       6 ahci
>     257 e1000e
>       6 ehci-pci
>    5891 nouveau
>      24 uhci_hcd
> 
> Does nouveau having this high number of DMA mapping is normal ?
Yeah seems perfectly fine for a gpu.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

On Wed, Aug 14, 2019 at 07:49:27PM +0200, Daniel Vetter
wrote:
> On Wed, Aug 14, 2019 at 04:50:33PM +0200, Corentin Labbe wrote:
> > Hello
> > 
> > Since lot of release (at least since 4.19), I hit the following error
message:
> > DMA-API: cacheline tracking ENOMEM, dma-debug disabled
> > 
> > After hitting that, I try to check who is creating so many DMA mapping
and see:
> > cat /sys/kernel/debug/dma-api/dump | cut -d' ' -f2 | sort |
uniq -c
> >       6 ahci
> >     257 e1000e
> >       6 ehci-pci
> >    5891 nouveau
> >      24 uhci_hcd
> > 
> > Does nouveau having this high number of DMA mapping is normal ?
> 
> Yeah seems perfectly fine for a gpu.
That is a lot and apparently overwhelm the dma-debug tracking.  Robin
rewrote this code in Linux 4.21 to work a little better, so I'm curious
why this might have changes in 4.19, as dma-debug did not change at
all there.

On Wed, Aug 14, 2019 at 07:49:27PM +0200, Daniel Vetter
wrote:
> On Wed, Aug 14, 2019 at 04:50:33PM +0200, Corentin Labbe wrote:
> > Hello
> > 
> > Since lot of release (at least since 4.19), I hit the following error
message:
> > DMA-API: cacheline tracking ENOMEM, dma-debug disabled
> > 
> > After hitting that, I try to check who is creating so many DMA mapping
and see:
> > cat /sys/kernel/debug/dma-api/dump | cut -d' ' -f2 | sort |
uniq -c
> >       6 ahci
> >     257 e1000e
> >       6 ehci-pci
> >    5891 nouveau
> >      24 uhci_hcd
> > 
> > Does nouveau having this high number of DMA mapping is normal ?
> 
> Yeah seems perfectly fine for a gpu.
Note that it never go down and when I terminate my X session, it stays the same.
So without any "real" GPU work, does it is still normal to have so
many active mapping ?

For example, when doing some transfer, the ahci mapping number changes and then
always go down to 6.