From nobody Thu Dec 18 20:19:31 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B880819ABC2 for ; Wed, 18 Dec 2024 11:16:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734520590; cv=none; b=rcJ6FGCj8lz4itcTtRz77kxbw/EJvsMLypSlLTzPVaTixdu1WixuRjTbgrfUqQo9J2l3LzuQG28lmsyK73zlcbuI6BAAoC6n9zZn1UM2M7TA6VFa3YK5oy1Bdt/xlp+y9KbZHpEGimwawQrOyBvSReFUhD0GcWZGCSDgdy3Qa0g= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734520590; c=relaxed/simple; bh=KHeSjPd0zRCAGUtxGFlcWOPrmx9y+ukDcIFpzj3jkJU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VNFn9to8t0wOD8IXb7Sc3B2h+2d87qSZVI88H31oPaiRNrqI+grCH9wDZ5jaUf3+Egir+2K9jLi0FAPNqjas45OEKHOduFLMYt+ORnwdXSeaO2Dcoy7aWFxX8sZmn7Obp27DnF8V5o9YTZRdnkIQk3khGleNnWrmVuWWR066fOk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=1NegcJlp; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=8VFfZVdq; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="1NegcJlp"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="8VFfZVdq" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1734520586; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XOfEVIxyuzb94jSGu1mkbITIF88QTRaDLmkNO646qMs=; b=1NegcJlpKykNW1HiGWSvi9auFDlUOcVsa/R0nC8qJ0T3ic4JwNQf/vXiIjmOLXXhEdhVEg AZen1kwMZyepRnfPI+EznLQjn1nBqGU8qf/4PQrAoLC03ZwnsgSKu49SpgajzF6eryaWHZ G9Z6HN9eTw0yT0el5Dql7PpY/J/AljRSTK4jFr2zW9MZklQ1rUSQghHLCGvgStyFSJ50Kn X/QALxeQwKk5I5GG63AWWYGeGZ6co29h1ptEKpi5hQaKfu8hRboSLlK2W+KEGeKqg+Grhu Bk8Iu/4Hx4YW6vjnwuNck0XaNWPIKHTfl3UE1AaApJAPcakiimpk2rIihDr90w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1734520586; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XOfEVIxyuzb94jSGu1mkbITIF88QTRaDLmkNO646qMs=; b=8VFfZVdqwmI7NGr8ifOHzbbM2xZY7KdOSU2onWiSQ9d1QXTR+bswedr7JtDjEfoIYjjmX4 SNUqt69ZSp5/LqCA== To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Andr=C3=A9=20Almeida?= , Darren Hart , Davidlohr Bueso , Ingo Molnar , Juri Lelli , Peter Zijlstra , Thomas Gleixner , Valentin Schneider , Waiman Long , Sebastian Andrzej Siewior Subject: [PATCH v6 04/15] futex: Hash only the address for private futexes. Date: Wed, 18 Dec 2024 12:09:42 +0100 Message-ID: <20241218111618.268028-5-bigeasy@linutronix.de> In-Reply-To: <20241218111618.268028-1-bigeasy@linutronix.de> References: <20241218111618.268028-1-bigeasy@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" futex_hash() passes the whole futex_key to jhash2. The first two member are passed as the first argument and the offset as the "initial value". For private futexes, the mm-part is always the same and it is used only within the process. By excluding the mm part from the hash, we reduce the length passed to jhash2 from 4 (16 / 4) to 2 (8 / 2). This avoids the __jhash_mix() part of jhash. The resulting code is smaller and based on testing this variant performs as good as the original or slightly better. Signed-off-by: Sebastian Andrzej Siewior --- kernel/futex/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/futex/core.c b/kernel/futex/core.c index b87bd27b73707..583a0149d62c9 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -134,8 +134,8 @@ struct futex_hash_bucket *futex_hash(union futex_key *k= ey) if (fhb && futex_key_is_private(key)) { u32 hash_mask =3D current->mm->futex_hash_mask; =20 - hash =3D jhash2((u32 *)key, - offsetof(typeof(*key), both.offset) / 4, + hash =3D jhash2((void *)&key->private.address, + sizeof(key->private.address) / 4, key->both.offset); return &fhb[hash & hash_mask]; } --=20 2.45.2