* [PATCH] drm/i915/gvt: Optimize mmio_offset_compare() for efficiency
@ 2023-10-12 23:04 Kuan-Wei Chiu
2023-10-13 10:36 ` Ville Syrjälä
0 siblings, 1 reply; 3+ messages in thread
From: Kuan-Wei Chiu @ 2023-10-12 23:04 UTC (permalink / raw)
To: zhenyuw, zhi.a.wang
Cc: jani.nikula, joonas.lahtinen, rodrigo.vivi, tvrtko.ursulin,
airlied, daniel, intel-gvt-dev, intel-gfx, dri-devel,
linux-kernel, Kuan-Wei Chiu
The original code used conditional branching in the mmio_offset_compare
function to compare two values and return -1, 1, or 0 based on the
result. However, the list_sort comparison function only needs results
<0, >0, or =0. This patch optimizes the code to make the comparison
branchless, improving efficiency and reducing code size. This change
reduces the number of comparison operations from 1-2 to a single
subtraction operation, thereby saving the number of instructions.
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
drivers/gpu/drm/i915/gvt/debugfs.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/gvt/debugfs.c b/drivers/gpu/drm/i915/gvt/debugfs.c
index baccbf1761b7..998d82a259c8 100644
--- a/drivers/gpu/drm/i915/gvt/debugfs.c
+++ b/drivers/gpu/drm/i915/gvt/debugfs.c
@@ -48,11 +48,7 @@ static int mmio_offset_compare(void *priv,
ma = container_of(a, struct diff_mmio, node);
mb = container_of(b, struct diff_mmio, node);
- if (ma->offset < mb->offset)
- return -1;
- else if (ma->offset > mb->offset)
- return 1;
- return 0;
+ return ma->offset - mb->offset;
}
static inline int mmio_diff_handler(struct intel_gvt *gvt,
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] drm/i915/gvt: Optimize mmio_offset_compare() for efficiency
2023-10-12 23:04 [PATCH] drm/i915/gvt: Optimize mmio_offset_compare() for efficiency Kuan-Wei Chiu
@ 2023-10-13 10:36 ` Ville Syrjälä
2023-10-13 12:13 ` [PATCH v2] " Kuan-Wei Chiu
0 siblings, 1 reply; 3+ messages in thread
From: Ville Syrjälä @ 2023-10-13 10:36 UTC (permalink / raw)
To: Kuan-Wei Chiu
Cc: zhenyuw, zhi.a.wang, tvrtko.ursulin, intel-gvt-dev, intel-gfx,
linux-kernel, dri-devel, rodrigo.vivi
On Fri, Oct 13, 2023 at 07:04:49AM +0800, Kuan-Wei Chiu wrote:
> The original code used conditional branching in the mmio_offset_compare
> function to compare two values and return -1, 1, or 0 based on the
> result. However, the list_sort comparison function only needs results
> <0, >0, or =0. This patch optimizes the code to make the comparison
> branchless, improving efficiency and reducing code size. This change
> reduces the number of comparison operations from 1-2 to a single
> subtraction operation, thereby saving the number of instructions.
>
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
> drivers/gpu/drm/i915/gvt/debugfs.c | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/debugfs.c b/drivers/gpu/drm/i915/gvt/debugfs.c
> index baccbf1761b7..998d82a259c8 100644
> --- a/drivers/gpu/drm/i915/gvt/debugfs.c
> +++ b/drivers/gpu/drm/i915/gvt/debugfs.c
> @@ -48,11 +48,7 @@ static int mmio_offset_compare(void *priv,
>
> ma = container_of(a, struct diff_mmio, node);
> mb = container_of(b, struct diff_mmio, node);
> - if (ma->offset < mb->offset)
> - return -1;
> - else if (ma->offset > mb->offset)
> - return 1;
> - return 0;
> + return ma->offset - mb->offset;
Those are unsigned ints effectively, so this only works due
to the return value being the same size signed int. Might be
better to add some explicit casts.
> }
>
> static inline int mmio_diff_handler(struct intel_gvt *gvt,
> --
> 2.25.1
--
Ville Syrjälä
Intel
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH v2] drm/i915/gvt: Optimize mmio_offset_compare() for efficiency
2023-10-13 10:36 ` Ville Syrjälä
@ 2023-10-13 12:13 ` Kuan-Wei Chiu
0 siblings, 0 replies; 3+ messages in thread
From: Kuan-Wei Chiu @ 2023-10-13 12:13 UTC (permalink / raw)
To: ville.syrjala, zhenyuw, zhi.a.wang
Cc: jani.nikula, joonas.lahtinen, rodrigo.vivi, tvrtko.ursulin,
airlied, daniel, intel-gvt-dev, intel-gfx, dri-devel,
linux-kernel, Kuan-Wei Chiu
The original code used conditional branching in the mmio_offset_compare
function to compare two values and return -1, 1, or 0 based on the
result. However, the list_sort comparison function only needs results
<0, >0, or =0. This patch optimizes the code to make the comparison
branchless, improving efficiency and reducing code size. This change
reduces the number of comparison operations from 1-2 to a single
subtraction operation, thereby saving the number of instructions.
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
v1 -> v2:
- Add explicit type cast in case the sizes of u32 and int differ.
drivers/gpu/drm/i915/gvt/debugfs.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/gvt/debugfs.c b/drivers/gpu/drm/i915/gvt/debugfs.c
index baccbf1761b7..d85d8a3b5ae5 100644
--- a/drivers/gpu/drm/i915/gvt/debugfs.c
+++ b/drivers/gpu/drm/i915/gvt/debugfs.c
@@ -48,11 +48,7 @@ static int mmio_offset_compare(void *priv,
ma = container_of(a, struct diff_mmio, node);
mb = container_of(b, struct diff_mmio, node);
- if (ma->offset < mb->offset)
- return -1;
- else if (ma->offset > mb->offset)
- return 1;
- return 0;
+ return (int)ma->offset - (int)mb->offset;
}
static inline int mmio_diff_handler(struct intel_gvt *gvt,
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2023-10-12 23:04 [PATCH] drm/i915/gvt: Optimize mmio_offset_compare() for efficiency Kuan-Wei Chiu
2023-10-13 10:36 ` Ville Syrjälä
2023-10-13 12:13 ` [PATCH v2] " Kuan-Wei Chiu
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