Re: [PATCH net-next v1] tcp: remove redundant memset in hot paths with CONFIG_INIT_STACK_ALL_ZERO

[Jiayuan Chen <mrpre@163.com>]

On 3/12/26 8:53 PM, Eric Dumazet wrote:
> On Thu, Mar 12, 2026 at 1:48 PM Jiayuan Chen <jiayuan.chen@linux.dev> wrote:
>> Modern compilers with CONFIG_INIT_STACK_ALL_ZERO enabled
>> (-ftrivial-auto-var-init=zero) automatically zero-initialize all stack
>> variables via `rep stos` in the function prologue. However, the compiler
>> cannot eliminate explicit memset() calls on those same variables,
>> resulting in redundant zeroing of the same memory region.
>>
>> Replace explicit memset() with `= {0}` initializers for stack variables
>> in TCP hot path functions. With `= {0}`, the compiler recognizes a single
>> initialization and generates only one zeroing sequence, whereas a
>> separate memset() after declaration always produces a second `rep stos`.
> No sorry. It seems you missed
>
> commit cfcceb7a39fc10a6f896af8229bf81d96acb22cc
> Author: Keita Morisaki <kmta1236@gmail.com>
> Date:   Wed Mar 4 20:15:17 2026 +0900
>
>      tcp: shrink per-packet memset in __tcp_transmit_skb()
>
> No need to resend your patch, I do not think it is a good idea.
Thanks. It seems this patch for __tcp_transmit_skb only saves a few bytes
of memset.