From: "H. Peter Anvin" <hpa@zytor.com>
To: David Laight <david.laight.linux@gmail.com>,
Uros Bizjak <ubizjak@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH -tip 2/2] x86/hweight: Use POPCNT when available with X86_NATIVE_CPU option
Date: Sun, 30 Mar 2025 15:44:19 -0700 [thread overview]
Message-ID: <0C7D298A-86E7-427F-B45B-25C2F663D2FA@zytor.com> (raw)
In-Reply-To: <20250330191544.213e07d8@pumpkin>
On March 30, 2025 11:15:44 AM PDT, David Laight <david.laight.linux@gmail.com> wrote:
>On Sun, 30 Mar 2025 18:07:30 +0200
>Uros Bizjak <ubizjak@gmail.com> wrote:
>
>...
>> The kernel is currently compiled with -mno-red-zone, gcc-15 introduces
>> special "redzone" clobber to disable red-zone in the function that
>> includes asm() when/if the kernel starts using redzone.
>
>I really don't understand the point of a stack 'red-zone'.
>In any function that contains memory writes the cost of a
>'sub $n,%rsp' at the top and corresponding add at the bottom
>is surely noise.
>
> David.
Perhaps you should check out the performance numbers instead.
next prev parent reply other threads:[~2025-03-30 22:44 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-25 16:48 [PATCH -tip 1/2] x86/hweight: Fix false output register dependency of POPCNT insn Uros Bizjak
2025-03-25 16:48 ` [PATCH -tip 2/2] x86/hweight: Use POPCNT when available with X86_NATIVE_CPU option Uros Bizjak
2025-03-25 17:11 ` Borislav Petkov
2025-03-30 15:15 ` Uros Bizjak
2025-03-30 17:31 ` Borislav Petkov
2025-03-30 18:47 ` Ingo Molnar
2025-03-30 19:06 ` Borislav Petkov
2025-03-30 19:20 ` Ingo Molnar
2025-03-30 19:28 ` Borislav Petkov
2025-03-25 21:56 ` Ingo Molnar
2025-03-29 9:19 ` Uros Bizjak
2025-03-29 11:00 ` David Laight
2025-03-30 7:49 ` Uros Bizjak
2025-03-30 18:02 ` David Laight
2025-03-29 23:10 ` H. Peter Anvin
2025-03-30 6:54 ` Uros Bizjak
2025-03-30 9:56 ` Ingo Molnar
2025-03-30 16:07 ` Uros Bizjak
2025-03-30 18:15 ` David Laight
2025-03-30 22:44 ` H. Peter Anvin [this message]
2025-03-30 18:54 ` Ingo Molnar
2025-03-25 17:09 ` [PATCH -tip 1/2] x86/hweight: Fix false output register dependency of POPCNT insn Borislav Petkov
2025-03-25 17:17 ` Uros Bizjak
2025-03-25 17:44 ` Borislav Petkov
2025-03-25 21:50 ` Ingo Molnar
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