From nobody Wed Dec 17 19:59:43 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 8000919258C for ; Tue, 25 Feb 2025 17:09:29 +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=1740503371; cv=none; b=ImSYkUiVsxBTnh2HVd2C0vecLuZQLWTffISqr6WHI4iT4ukttI9aB0E5DdPpjvAuDOHBjUbjxZzqlcU0cGqLDNhk564Nx+FLt/P71W0XGsS5ADWw3DtZLLEfj9PtV8x98s9PsuBjxWWj9tb4ErpDo/mMj11Sr1ZaTz/MKuGw7xo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740503371; c=relaxed/simple; bh=z7SKTQ7Ma64q/SAOUM4xlnyQVGuryAeFCcdUA7KW4bI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UuESnIp94NvTp5R5ysE/Cm3AMKYDa/52wvOIRyDc7QFgnGMaNzWYcdMEkn+dyMbgDFNjhAceEGvBlb2EhXO50cOrun+CAZxDC6/XoT4ayasxICNP2S1npg1WYFt6/MM4bPSbL7hirMXcpYlI07TFp05a3INy8i1SUAvE+Ol7XLU= 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=KZKvLIIR; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=AoqM9zZb; 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="KZKvLIIR"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="AoqM9zZb" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1740503361; 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=rkKAJ4zyYXh6FJYQyMom9miYRg7bgz+h0w13kY0QJBI=; b=KZKvLIIR1P2O5E1vcCB1yqF0Cr8B6O6jgTeTQT8zyfsdv4uVG327uEpG9c3dCW5sCPd9sU lsJo+oib+Q8pd7m/e4p80X7k1NZqlEggx3cTRsCe9ZJET3WJOUofslVvll4lvd2L1TWZjF xA+biGrTRBr9Ij4KQreDtPlBf0+WnY5Esuo0SDpNJj8aY15IRp9nlPdMYbIxOKVafLNGMa CWZodrkkd9Ke7PFvBVwmpTZ44VwULDFaymKP24HgYb7oWM1udCu9+uSctcwUZYDifkq8Oj MPzi4o4FDFRgVtdx9alN7H+nMRFnZ4dGhtJoLrQHEANZVSH1+g0b1OytAy47pQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1740503361; 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=rkKAJ4zyYXh6FJYQyMom9miYRg7bgz+h0w13kY0QJBI=; b=AoqM9zZbFZey+sikzxRYPfDE8/qG9Mgw9tDuP6raihhKPvXLtEOYRP+6Py1Nax33XvEQPc GtiFpaa/5G6TF8Dw== 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 v9 04/11] futex: Hash only the address for private futexes. Date: Tue, 25 Feb 2025 18:09:07 +0100 Message-ID: <20250225170914.289358-5-bigeasy@linutronix.de> In-Reply-To: <20250225170914.289358-1-bigeasy@linutronix.de> References: <20250225170914.289358-1-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 | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) diff --git a/kernel/futex/core.c b/kernel/futex/core.c index e64a5cf818414..e4e0bc7722d78 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -117,6 +117,18 @@ static inline bool futex_key_is_private(union futex_ke= y *key) return !(key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED)); } =20 +static struct futex_hash_bucket *futex_hash_private(union futex_key *key, + struct futex_hash_bucket *fhb, + u32 hash_mask) +{ + u32 hash; + + hash =3D jhash2((void *)&key->private.address, + sizeof(key->private.address) / 4, + key->both.offset); + return &fhb[hash & hash_mask]; +} + /** * futex_hash - Return the hash bucket in the global or local hash * @key: Pointer to the futex key for which the hash is calculated @@ -131,14 +143,9 @@ struct futex_hash_bucket *__futex_hash(union futex_key= *key) u32 hash; =20 fhb =3D current->mm->futex_hash_bucket; - if (fhb && futex_key_is_private(key)) { - u32 hash_mask =3D current->mm->futex_hash_mask; + if (fhb && futex_key_is_private(key)) + return futex_hash_private(key, fhb, current->mm->futex_hash_mask); =20 - hash =3D jhash2((u32 *)key, - offsetof(typeof(*key), both.offset) / 4, - key->both.offset); - return &fhb[hash & hash_mask]; - } hash =3D jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4, key->both.offset); --=20 2.47.2