Re: [PATCH 2/2] futex: Use atomic64_try_cmpxchg_relaxed() in get_inode_sequence_number()

[André Almeida]

Em 10/10/2024 04:10, Uros Bizjak escreveu:
> Optimize get_inode_sequence_number() to use simpler and faster:
>
>    !atomic64_try_cmpxchg_relaxed(*ptr, &old, new)
>
> instead of:
>
>    atomic64_cmpxchg relaxed(*ptr, old, new) != old
>
> The x86 CMPXCHG instruction returns success in ZF flag, so
> this change saves a compare after cmpxchg. The generated
> code improves from:
>
>   3da:	31 c0                	xor    %eax,%eax
>   3dc:	f0 48 0f b1 8a 38 01 	lock cmpxchg %rcx,0x138(%rdx)
>   3e3:	00 00
>   3e5:	48 85 c0             	test   %rax,%rax
>   3e8:	48 0f 44 c1          	cmove  %rcx,%rax
>
> to:
>
>   3da:	31 c0                	xor    %eax,%eax
>   3dc:	f0 48 0f b1 8a 38 01 	lock cmpxchg %rcx,0x138(%rdx)
>   3e3:	00 00
>   3e5:	48 0f 44 c1          	cmove  %rcx,%rax
>
> Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> Cc: "André Almeida" <andrealmeid@xxxxxxxxxx>

Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxx>