2024-06-13 07:36:40

by Qingfang Deng

Subject: [PATCH net-next] etherdevice: Optimize is_broadcast_ether_addr

From: Qingfang Deng <[email protected]>

Like is_zero_ether_addr, is_broadcast_ether_addr can also be optimized
by using a 32-bit load if CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is set.
Sign extension is used to populate the upper 16-bit of the 16-bit load.

Signed-off-by: Qingfang Deng <[email protected]>
---
include/linux/etherdevice.h | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
index 2ad1ffa4ccb9..23b9cc5e299d 100644
--- a/include/linux/etherdevice.h
+++ b/include/linux/etherdevice.h
@@ -174,9 +174,14 @@ static inline bool is_local_ether_addr(const u8 *addr)
*/
static inline bool is_broadcast_ether_addr(const u8 *addr)
{
+#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+ return (*(const s32 *)(addr + 0) &
+ *(const s16 *)(addr + 4)) == (s32)0xffffffff;
+#else
return (*(const u16 *)(addr + 0) &
*(const u16 *)(addr + 2) &
*(const u16 *)(addr + 4)) == 0xffff;
+#endif
}

/**
--
2.34.1

2024-06-14 00:05:44

by Jakub Kicinski

Subject: Re: [PATCH net-next] etherdevice: Optimize is_broadcast_ether_addr

On Thu, 13 Jun 2024 15:34:41 +0800 Qingfang Deng wrote:
> Like is_zero_ether_addr, is_broadcast_ether_addr can also be optimized
> by using a 32-bit load if CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is set.
> Sign extension is used to populate the upper 16-bit of the 16-bit load.

Can you provide more context on why it's beneficial. I mean, there's a
lot of code in the kernel one could micro-optimize...

Show us the assembly, cycle counts, where it's used on fast paths...
--
pw-bot: cr