Re: [PATCH] drm/amd/debugfs: Expose GFXOFF state to userspace

[Alex Deucher]

On Thu, Jul 14, 2022 at 12:45 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote:
>
>
>
> Às 13:42 de 14/07/22, Alex Deucher escreveu:
> > On Wed, Jul 13, 2022 at 11:15 AM André Almeida <andrealmeid@xxxxxxxxxx> wrote:
> >>
> >> GFXOFF has two different "state" values: one to define if the GPU is
> >> allowed/disallowed to enter GFXOFF, usually called state; and another
> >> one to define if currently GFXOFF is being used, usually called status.
> >> Even when GFXOFF is allowed, GPU firmware can decide to not used it
> >> accordingly to the GPU load.
> >>
> >> Userspace can allow/disallow GPUs to enter into GFXOFF via debugfs. The
> >> kernel maintains a counter of requests for GFXOFF (gfx_off_req_count)
> >> that should be decreased to allow GFXOFF and increased to disallow.
> >>
> >> The issue with this interface is that userspace can't be sure if GFXOFF
> >> is currently allowed. Even by checking amdgpu_gfxoff file, one might get
> >> an ambiguous 2, that means that GPU is currently out of GFXOFF, but that
> >> can be either because it's currently disallowed or because it's allowed
> >> but given the current GPU load it's enabled. Then, userspace needs to
> >> rely on the fact that GFXOFF is enabled by default on boot and to track
> >> this information.
> >>
> >> To make userspace life easier and GFXOFF more reliable, return the
> >> current state of GFXOFF to userspace when reading amdgpu_gfxoff with the
> >> same semantics of writing: 0 means not allowed, not 0 means allowed.
> >>
> >
> > This looks good. Can you document this in the amdgpu kerneldoc?
> >
>
> Sure, let me send a v2 with that

While you are at it, if we are missing docs for the other gfxoff file
can you add that as well?

Thanks!

Alex

>
> > Alex
> >
> >> Expose the current status of GFXOFF through a new file,
> >> amdgpu_gfxoff_status.
> >>
> >> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
> >> ---
> >>  drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 49 ++++++++++++++++++++-
> >>  1 file changed, 47 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> >> index f3b3c688e4e7..e2eec985adb3 100644
> >> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> >> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> >> @@ -1117,13 +1117,50 @@ static ssize_t amdgpu_debugfs_gfxoff_read(struct file *f, char __user *buf,
> >>         }
> >>
> >>         while (size) {
> >> -               uint32_t value;
> >> +               u32 value = adev->gfx.gfx_off_state;
> >> +
> >> +               r = put_user(value, (u32 *)buf);
> >> +               if (r)
> >> +                       goto out;
> >> +
> >> +               result += 4;
> >> +               buf += 4;
> >> +               *pos += 4;
> >> +               size -= 4;
> >> +       }
> >> +
> >> +       r = result;
> >> +out:
> >> +       pm_runtime_mark_last_busy(adev_to_drm(adev)->dev);
> >> +       pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
> >> +
> >> +       return r;
> >> +}
> >> +
> >> +static ssize_t amdgpu_debugfs_gfxoff_status_read(struct file *f, char __user *buf,
> >> +                                                size_t size, loff_t *pos)
> >> +{
> >> +       struct amdgpu_device *adev = file_inode(f)->i_private;
> >> +       ssize_t result = 0;
> >> +       int r;
> >> +
> >> +       if (size & 0x3 || *pos & 0x3)
> >> +               return -EINVAL;
> >> +
> >> +       r = pm_runtime_get_sync(adev_to_drm(adev)->dev);
> >> +       if (r < 0) {
> >> +               pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
> >> +               return r;
> >> +       }
> >> +
> >> +       while (size) {
> >> +               u32 value;
> >>
> >>                 r = amdgpu_get_gfx_off_status(adev, &value);
> >>                 if (r)
> >>                         goto out;
> >>
> >> -               r = put_user(value, (uint32_t *)buf);
> >> +               r = put_user(value, (u32 *)buf);
> >>                 if (r)
> >>                         goto out;
> >>
> >> @@ -1206,6 +1243,12 @@ static const struct file_operations amdgpu_debugfs_gfxoff_fops = {
> >>         .llseek = default_llseek
> >>  };
> >>
> >> +static const struct file_operations amdgpu_debugfs_gfxoff_status_fops = {
> >> +       .owner = THIS_MODULE,
> >> +       .read = amdgpu_debugfs_gfxoff_status_read,
> >> +       .llseek = default_llseek
> >> +};
> >> +
> >>  static const struct file_operations *debugfs_regs[] = {
> >>         &amdgpu_debugfs_regs_fops,
> >>         &amdgpu_debugfs_regs2_fops,
> >> @@ -1217,6 +1260,7 @@ static const struct file_operations *debugfs_regs[] = {
> >>         &amdgpu_debugfs_wave_fops,
> >>         &amdgpu_debugfs_gpr_fops,
> >>         &amdgpu_debugfs_gfxoff_fops,
> >> +       &amdgpu_debugfs_gfxoff_status_fops,
> >>  };
> >>
> >>  static const char *debugfs_regs_names[] = {
> >> @@ -1230,6 +1274,7 @@ static const char *debugfs_regs_names[] = {
> >>         "amdgpu_wave",
> >>         "amdgpu_gpr",
> >>         "amdgpu_gfxoff",
> >> +       "amdgpu_gfxoff_status",
> >>  };
> >>
> >>  /**
> >> --
> >> 2.37.0
> >>