[PATCH] ARC: unwind: Use built-in sort swap to reduce code size and improve performance

[PATCH] ARC: unwind: Use built-in sort swap to reduce code size and improve performance

[Yu-Chun Lin]

The custom swap function used in sort() was identical to the default
built-in sort swap. Remove the custom swap function and passes NULL to
sort(), allowing it to use the default swap function.

This change reduces code size and improves performance, particularly when
CONFIG_MITIGATION_RETPOLINE is enabled. With RETPOLINE mitigation, indirect
function calls incur significant overhead, and using the default swap
function avoids this cost.

$ ./scripts/bloat-o-meter ./unwind.o.old ./unwind.o.new
add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-22 (-22)
Function                                     old     new   delta
init_unwind_hdr.constprop                    544     540      -4
swap_eh_frame_hdr_table_entries               18       -     -18
Total: Before=4410, After=4388, chg -0.50%

Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
---
Compile test only

 arch/arc/kernel/unwind.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/arch/arc/kernel/unwind.c b/arch/arc/kernel/unwind.c
index d8969dab12d4..789cfb9ea14e 100644
--- a/arch/arc/kernel/unwind.c
+++ b/arch/arc/kernel/unwind.c
@@ -241,15 +241,6 @@ static int cmp_eh_frame_hdr_table_entries(const void *p1, const void *p2)
 	return (e1->start > e2->start) - (e1->start < e2->start);
 }
 
-static void swap_eh_frame_hdr_table_entries(void *p1, void *p2, int size)
-{
-	struct eh_frame_hdr_table_entry *e1 = p1;
-	struct eh_frame_hdr_table_entry *e2 = p2;
-
-	swap(e1->start, e2->start);
-	swap(e1->fde, e2->fde);
-}
-
 static void init_unwind_hdr(struct unwind_table *table,
 			    void *(*alloc) (unsigned long))
 {
@@ -345,7 +336,7 @@ static void init_unwind_hdr(struct unwind_table *table,
 	sort(header->table,
 	     n,
 	     sizeof(*header->table),
-	     cmp_eh_frame_hdr_table_entries, swap_eh_frame_hdr_table_entries);
+	     cmp_eh_frame_hdr_table_entries, NULL);
 
 	table->hdrsz = hdrSize;
 	smp_wmb();
-- 
2.43.0


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Re: [PATCH] ARC: unwind: Use built-in sort swap to reduce code size and improve performance

[Vineet Gupta]

On 4/9/25 10:11, Yu-Chun Lin wrote:
> The custom swap function used in sort() was identical to the default
> built-in sort swap. Remove the custom swap function and passes NULL to
> sort(), allowing it to use the default swap function.
>
> This change reduces code size and improves performance, particularly when
> CONFIG_MITIGATION_RETPOLINE is enabled. With RETPOLINE mitigation, indirect
> function calls incur significant overhead, and using the default swap
> function avoids this cost.
>
> $ ./scripts/bloat-o-meter ./unwind.o.old ./unwind.o.new
> add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-22 (-22)
> Function                                     old     new   delta
> init_unwind_hdr.constprop                    544     540      -4
> swap_eh_frame_hdr_table_entries               18       -     -18
> Total: Before=4410, After=4388, chg -0.50%
>
> Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>

Acked-by: Vineet Gupta <vgupta@kernel.org>

Added to for-curr.

Thx,
-Vineet

> ---
> Compile test only
>
>  arch/arc/kernel/unwind.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
>
> diff --git a/arch/arc/kernel/unwind.c b/arch/arc/kernel/unwind.c
> index d8969dab12d4..789cfb9ea14e 100644
> --- a/arch/arc/kernel/unwind.c
> +++ b/arch/arc/kernel/unwind.c
> @@ -241,15 +241,6 @@ static int cmp_eh_frame_hdr_table_entries(const void *p1, const void *p2)
>  	return (e1->start > e2->start) - (e1->start < e2->start);
>  }
>  
> -static void swap_eh_frame_hdr_table_entries(void *p1, void *p2, int size)
> -{
> -	struct eh_frame_hdr_table_entry *e1 = p1;
> -	struct eh_frame_hdr_table_entry *e2 = p2;
> -
> -	swap(e1->start, e2->start);
> -	swap(e1->fde, e2->fde);
> -}
> -
>  static void init_unwind_hdr(struct unwind_table *table,
>  			    void *(*alloc) (unsigned long))
>  {
> @@ -345,7 +336,7 @@ static void init_unwind_hdr(struct unwind_table *table,
>  	sort(header->table,
>  	     n,
>  	     sizeof(*header->table),
> -	     cmp_eh_frame_hdr_table_entries, swap_eh_frame_hdr_table_entries);
> +	     cmp_eh_frame_hdr_table_entries, NULL);
>  
>  	table->hdrsz = hdrSize;
>  	smp_wmb();


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