| Message ID | 20231012230449.2109078-1-visitorckw@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915/gvt: Optimize mmio_offset_compare() for efficiency | expand |
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
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,
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(-)