From nobody Wed Dec 17 19:52:38 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 8F20A1885A5 for ; Sun, 15 Dec 2024 23:06:54 +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=1734304016; cv=none; b=YQMhXxO9oznLjYtEl/mNlwAFUsxl7N3V3T3y5NLMS4qAj4XQZtI/1sYKwIKJB+JIahnpehtRauEL7Ls1bIuEWgpNrcMtvNwz9R5c5idpzvLOR6jKGXHjGWY23UUSFaJ+vjQSDb+CfQ1RY6UN2e59wcAwdRqLWdHsKfupBph51bU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734304016; c=relaxed/simple; bh=KHeSjPd0zRCAGUtxGFlcWOPrmx9y+ukDcIFpzj3jkJU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YdphbcoZP6xBF0NDQndhO/l9CGCu/Jh0woBjqwiQZhsxM7u337sJrvV1ECN1CQh23BZ4JHyIt0NAJ8Znc0FhpmhDw5oLLNqkWOulOt+YVQ6iHjyF+82tZDVV7JGxvO6XwrS6L4Ya1DFJRJ9JyHZxGiIIdydc50j2QHtbpc9A07I= 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=Wj1RtPGw; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ROwnjMX9; 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="Wj1RtPGw"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ROwnjMX9" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1734304007; 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=Wj1RtPGwGqK4iS882X2utHk7Xonbp1mBivUjy0D1YuCupWOe/9vnnbBqZJCOap/LzbNHUk TyDSggtUpL5IVLMO6RjPOvn3/g/kqQHETd+yvdMGvQK6dEDbdh8L0I9UyWb8SytEhXbUlp LqrTGnFqYe1R9TuI5YVgEUduV3+Sc1HJWLyJl+nHxQf/KOUgu+hEa92D2oeCIfNQ+05WFa Qyiqt8sW2PbOlK7jmSUcKJqro7XRU6LH4kKOX6kRw0QVnNjAwX242Y4kwfs/HWwCCYxc8D fBT1tLwiZGJtpfhj/SnUF/81fbibzp1GrdzbTKLd13rxYdTq0v38+wT527AXRg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1734304007; 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=ROwnjMX9Pjj3paSZUe1UCai39B5ThLmwtZ6/SrGAB75Vpz+807rKiO18QToxYefKGfymJi n6YQfDa9AKSAgnAg== 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 v5 04/14] futex: Hash only the address for private futexes. Date: Mon, 16 Dec 2024 00:00:08 +0100 Message-ID: <20241215230642.104118-5-bigeasy@linutronix.de> In-Reply-To: <20241215230642.104118-1-bigeasy@linutronix.de> References: <20241215230642.104118-1-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