From nobody Tue Feb 10 00:57:44 2026 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 B3C9A2063E7 for ; Mon, 3 Feb 2025 13:59:49 +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=1738591192; cv=none; b=OPaf/6y1PmgMoQ5WlVPDUnVPakSr6/P12VSteEd+jNdA32UAHEmlDyrw+FgtP2yAZ9S3WATy50R/9MDMWWJhEbQw2pGTk6oPFQGVTHnvpeH/WbENpenMFbl2RhGAFu+CzRXH5D62F0XEqD1eNoit2+Z+4oLaY0Q/wkIPr9dQHpk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738591192; c=relaxed/simple; bh=X5pzFQl3t9Id8Bg4N9Vu+xtYMPukwkaSLyljCfYdojQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YG84t3UK3xdmfgXmR/BA3RsfdKDW5lr+vaviBRMTfhsujSxSTLg/9v6mAPeqCXhb2Q4bp3KlWIPQyRxLzkiKqd3plku3LZjJpoBgj9gUG5HD703H2eGBlsYT1aBv31p2deJuejClLa2ns08JymziArn09AkVICunChTTf9rvjgE= 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=qTF8fUgb; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=19w4cvjf; 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="qTF8fUgb"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="19w4cvjf" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1738591186; 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=2Fblq5lzhRPvME3UqTEQiFKUL0jlzsGIai//ftQqLlw=; b=qTF8fUgbbogNRKtUjm6PiwG8FLHKBa0NMt4mUi66jfERsAGoYbVPibbQyMMWvhUBjZmnCI hjwVRb346ZA5v2kSz8X8M39SluyvekwvOCufRhmGA8q7rXl/MRWm+mA4BeTEaMpp0E/2Cg 0ELtek18NqozhrB+CTBk58T2T+JRTtbwzo8UGmS47NBOnp9aqXSJIJUAzJRTCP95Mvi9Q2 GFrH90yuxGb/eFPbUpXPPqGwcEv8O03Dkh8ycnBF3LPB+lW9xzQQjdRnfFPUrDX1k4I/F7 Yr+j+TThohsl2F3pLlFe68OrYNK0ZLsvPZlNQFh6unL770CKJiVRj6PXT6cF0A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1738591186; 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=2Fblq5lzhRPvME3UqTEQiFKUL0jlzsGIai//ftQqLlw=; b=19w4cvjfd6yy0uf7CrSFn47Uu+Iu/R/9ZGUthPVkqVDrbveouATshVn/EMC0kKY4R+4l0u vl/eZ7GJLHxMEqAA== 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 v8 05/15] futex: Hash only the address for private futexes. Date: Mon, 3 Feb 2025 14:59:25 +0100 Message-ID: <20250203135935.440018-6-bigeasy@linutronix.de> In-Reply-To: <20250203135935.440018-1-bigeasy@linutronix.de> References: <20250203135935.440018-1-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 26328d8072fee..f608cd6ccc032 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 2.47.2