linux-kernel - Re: [PATCH 2/2] drm/i915/gvt: Avoid full proxy f_ops for vgpu

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Message-ID: <Y72zVXYLVHXuyK05@intel.com>
Date:   Tue, 10 Jan 2023 13:49:57 -0500
From:   Rodrigo Vivi <rodrigo.vivi@...el.com>
To:     Deepak R Varma <drv@...lo.com>
CC:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        "Daniel Vetter" <daniel@...ll.ch>,
        <intel-gvt-dev@...ts.freedesktop.org>,
        <intel-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Saurabh Singh Sengar <ssengar@...rosoft.com>
Subject: Re: [PATCH 2/2] drm/i915/gvt: Avoid full proxy f_ops for vgpu_status
 debug attributes

On Wed, Jan 11, 2023 at 12:00:12AM +0530, Deepak R Varma wrote:
> Using DEFINE_SIMPLE_ATTRIBUTE macro with the debugfs_create_file()
> function adds the overhead of introducing a proxy file operation
> functions to wrap the original read/write inside file removal protection
> functions. This adds significant overhead in terms of introducing and
> managing the proxy factory file operations structure and function
> wrapping at runtime.
> As a replacement, a combination of DEFINE_DEBUGFS_ATTRIBUTE macro paired
> with debugfs_create_file_unsafe() is suggested to be used instead.  The
> DEFINE_DEBUGFS_ATTRIBUTE utilises debugfs_file_get() and
> debugfs_file_put() wrappers to protect the original read and write
> function calls for the debug attributes. There is no need for any
> runtime proxy file operations to be managed by the debugfs core.
> Following coccicheck make command helped identify this change:
> 
> make coccicheck M=drivers/gpu/drm/i915/ MODE=patch COCCI=./scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> 
> Signed-off-by: Deepak R Varma <drv@...lo.com>

I believe these 2 gvt cases could be done in one patch.
But anyways,

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@...el.com>

for both patches... and will leave these 2 patches for gvt folks
to apply. Unless they ack and I apply in the drm-intel along with the other ones.

> ---
>  drivers/gpu/drm/i915/gvt/debugfs.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/debugfs.c b/drivers/gpu/drm/i915/gvt/debugfs.c
> index 03f081c3d9a4..baccbf1761b7 100644
> --- a/drivers/gpu/drm/i915/gvt/debugfs.c
> +++ b/drivers/gpu/drm/i915/gvt/debugfs.c
> @@ -165,7 +165,7 @@ static int vgpu_status_get(void *data, u64 *val)
>  	return 0;
>  }
>  
> -DEFINE_SIMPLE_ATTRIBUTE(vgpu_status_fops, vgpu_status_get, NULL, "0x%llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(vgpu_status_fops, vgpu_status_get, NULL, "0x%llx\n");
>  
>  /**
>   * intel_gvt_debugfs_add_vgpu - register debugfs entries for a vGPU
> @@ -182,8 +182,8 @@ void intel_gvt_debugfs_add_vgpu(struct intel_vgpu *vgpu)
>  			    &vgpu_mmio_diff_fops);
>  	debugfs_create_file_unsafe("scan_nonprivbb", 0644, vgpu->debugfs, vgpu,
>  				   &vgpu_scan_nonprivbb_fops);
> -	debugfs_create_file("status", 0644, vgpu->debugfs, vgpu,
> -			    &vgpu_status_fops);
> +	debugfs_create_file_unsafe("status", 0644, vgpu->debugfs, vgpu,
> +				   &vgpu_status_fops);
>  }
>  
>  /**
> -- 
> 2.34.1
> 
> 
>