linux-kernel - Re: [PATCH] drm/vgm: replace idr_init() by idr_init

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Message-ID: <20201105103116.GA29881@localhost>
Date:   Thu, 5 Nov 2020 16:01:16 +0530
From:   Deepak R Varma <mh12gx2825@...il.com>
To:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     daniel@...ll.ch, mh12gx2825@...il.com
Subject: Re: [PATCH] drm/vgm: replace idr_init() by idr_init_base()

On Thu, Nov 05, 2020 at 10:42:15AM +0100, Daniel Vetter wrote:
> On Wed, Nov 04, 2020 at 04:53:38PM +0530, Deepak R Varma wrote:
> > idr_init() uses base 0 which is an invalid identifier. The new function
> > idr_init_base allows IDR to set the ID lookup from base 1. This avoids
> > all lookups that otherwise starts from 0 since 0 is always unused.
> > 
> > References: commit 6ce711f27500 ("idr: Make 1-based IDRs more efficient")
> > 
> > Signed-off-by: Deepak R Varma <mh12gx2825@...il.com>
> 
> Tiny typo in the commit message summary: s/vgm/vgem/
> 
> Also can you pls resbumit this with intel-gfx mailing list on cc (like for
> i915)? There's a CI bot there which runs a few vgem tests, would be good
> to confirm nothing has been broken.

Hi Daniel,
sure. I will correct the summary typo and also feed it to the CI bot.

Also, according to Felix Kuehling's comment on a similar patch for
drm/amdkfd driver, an ID can be 0. The change I am proposing is more
efficient for conditions that do not want to use ID as 0. Otherwise,
id = 0 is an acceptable possibility. So, my statement that "Id 0 is an invalid
identifier" is not true.

Can you please comment if this is accurate and I should reword my log
message as well?

Thank you.
./drv

> 
> Otherwise lgtm.
> 
> Thanks, Daniel
> 
> > ---
> >  drivers/gpu/drm/vgem/vgem_fence.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/vgem/vgem_fence.c b/drivers/gpu/drm/vgem/vgem_fence.c
> > index 17f32f550dd9..2902dc6e64fa 100644
> > --- a/drivers/gpu/drm/vgem/vgem_fence.c
> > +++ b/drivers/gpu/drm/vgem/vgem_fence.c
> > @@ -233,7 +233,7 @@ int vgem_fence_signal_ioctl(struct drm_device *dev,
> >  int vgem_fence_open(struct vgem_file *vfile)
> >  {
> >  	mutex_init(&vfile->fence_mutex);
> > -	idr_init(&vfile->fence_idr);
> > +	idr_init_base(&vfile->fence_idr, 1);
> >  
> >  	return 0;
> >  }
> > -- 
> > 2.25.1
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch