From nobody Thu Oct 9 07:19:54 2025 Received: from mail-pg1-f176.google.com (mail-pg1-f176.google.com [209.85.215.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 35EFD30E83A for ; Thu, 19 Jun 2025 18:26:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.176 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750357594; cv=none; b=lsvxxfPpGzU1NeZY0ARw7EoxTDF9E6s3bu3o3OREXRbAU5OcFSuxv+HiIGc05wYst75zQ9/y4m57UZo1eG+c770+cL9c1dfG4t10MK/flUtGXYJ9o6PQhhfcFg0HjdwdixKoKtdwehdLttTSfmgMlg+6FdJMBCVBLj/VoGjQU8Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750357594; c=relaxed/simple; bh=bf1eMts74yu7D6jH10IbTGmC2cX2IccfD+cBF9tFEzI=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=G1Dn9SClO5FQesbQ+8cmEvTsTrjQ69zBok0Mi33iBF6+mmcnuh/sz+oTj86HibZeK9Kg4wQaS0Il+VtQiXbpL2CddkQP14c5TSQzpotILyLT8Lf76jlqCbEY3GJQfilmloq1z04uKl8QqUX5dXlcbQiTptyRpzbIkOi3FujCSQk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=XKsyGwrb; arc=none smtp.client-ip=209.85.215.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="XKsyGwrb" Received: by mail-pg1-f176.google.com with SMTP id 41be03b00d2f7-b26f5f47ba1so842401a12.1 for ; Thu, 19 Jun 2025 11:26:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1750357592; x=1750962392; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:from:to:cc:subject:date:message-id :reply-to; bh=8WPFXPV0QkN55EuX7D7xMkc3nzc5+JHVWmC+JzqRihU=; b=XKsyGwrbuLN89VD3UtUh6iQ7UiVWm2Y00AnygEKMRLjdypBCu7eCRdPsT6IGnDRUZk pwgl89HyTlkp4SS1gSfw/gUuWaZN9ILi0wIK6/vqe8/ebqumbQuw02ELouXCWdJUpadR cdKHC6uKyB6ZPCYUbts/ytJ7E8TBFwSVkwVprnU5Wl+R6bBVpRAd2tKfl+kEZ8oYBpXH f3WFBRp0WOaFEXGvCXmm69kZnlBQmJQ6jduvkWB/xlwdafq+sIaFEOyt14eLWtImq4Of ZSUQltMLxSkXQq4e+AxrMSEE7H+VQdVNjWi59BVJkyH4e1xb4pFmCmChrjZcwq6TqxsL 81SA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750357592; x=1750962392; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=8WPFXPV0QkN55EuX7D7xMkc3nzc5+JHVWmC+JzqRihU=; b=DHYVtl24c8pBgDkPamQ2cAz8HciYbmAxfeiYkFiXgohI+qLMKrT5I40fbxidJFGQna BKlGXYUMJwMafciLBhpi8qi5kE9K8LmwN/DN2Vx49w14WezbZRiDt95Q+eIy4xSDl8Zu qw1H2E+pC+9/v5lz23hGNI/zNZwCEeuCpovShybgrRJQxswCNz0dOEuSqWXriKZehCCj rUI3GTQNgla6Mgxu04J/ZIWcRFaRQofNq9qncRDc/ZcPYtBzk4g9vVONVGOqRrQqdvU/ H2VHf7rmV4FQ7jb3qMuDScFEjSat/ci+z6f3v0v2pjB7G8GUbC/f2S59mrmaJKEkW9AK AYew== X-Gm-Message-State: AOJu0YyGRabbuDVxb5P5fCZXhI3GPNjndnE3clxvksTUYNhAnqOeMLpj Pyd/32fb/EpIYw4FPu0P7SMDaz6l9hzFzesP6Ki7eOllg5XkSbtnssgTWl49OQ== X-Gm-Gg: ASbGnctEnhMphtJuLi45TKroLn79nZgmkpMDM1Lsryw/HEV2TWZRHmwRnN9vUqhtVpG Q8GUzK1Fo4Zf7iYHiQLRXbdJU+J0AQwK02OBqCEYz1e9TB5MbQg2Cos1yD4qOXqZ7g0qp3Vn/Tr 8n+lbSvhd2+9cL6PcxujumXiorV1ayA0iOxwDsumnxf2K/7lpaPQcEc9VRSq2AROfGl1xMgSqP9 7rXZcTKpNmJOIKJD9SH3180HZz3U1iAUBg77K3LOnGGxFFAHCrr/e42viqMza9XilzPWZpreDQ5 djk1NwyE21+GByqQp1UjK7Fvm3NVqxyfb2qEZplKvnVCukYI50DWBJrMYJ76uQ== X-Google-Smtp-Source: AGHT+IFdc0iBbedgfsZ+dY9PEnKDY20nUmlAE+YJlV+4+gEVEjwwMq3o1XOE5bIAo96BlbzWR86Stw== X-Received: by 2002:a17:90b:3e86:b0:311:d05c:936 with SMTP id 98e67ed59e1d1-3159d8c8c1bmr400952a91.17.1750357592503; Thu, 19 Jun 2025 11:26:32 -0700 (PDT) Received: from localhost ([216.228.127.128]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3158a331983sm2532278a91.47.2025.06.19.11.26.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jun 2025 11:26:31 -0700 (PDT) From: Yury Norov To: linux-kernel@vger.kernel.org, "Yury Norov [NVIDIA]" , Rasmus Villemoes , John Stultz , Thomas Gleixner , Stephen Boyd , Andrew Morton Subject: [PATCH v4 1/3] bitmap: generalize node_random() Date: Thu, 19 Jun 2025 14:26:23 -0400 Message-ID: <20250619182626.393541-2-yury.norov@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250619182626.393541-1-yury.norov@gmail.com> References: <20250619182626.393541-1-yury.norov@gmail.com> 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" From: "Yury Norov [NVIDIA]" Generalize node_random() and make it available to general bitmaps and cpumasks users. Notice, find_first_bit() is generally faster than find_nth_bit(), and we employ it when there's a single set bit in the bitmap. See commit 3e061d924fe9c7b4 ("lib/nodemask: optimize node_random for nodemask with single NUMA node"). Signed-off-by: Yury Norov [NVIDIA] --- include/linux/find.h | 2 ++ include/linux/nodemask.h | 18 +++--------------- lib/find_bit.c | 24 ++++++++++++++++++++++++ 3 files changed, 29 insertions(+), 15 deletions(-) diff --git a/include/linux/find.h b/include/linux/find.h index 5a2c267ea7f9..98c61838002c 100644 --- a/include/linux/find.h +++ b/include/linux/find.h @@ -44,6 +44,8 @@ unsigned long _find_next_bit_le(const unsigned long *addr= , unsigned long size, unsigned long offset); #endif =20 +unsigned long find_random_bit(const unsigned long *addr, unsigned long siz= e); + #ifndef find_next_bit /** * find_next_bit - find the next set bit in a memory region diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h index 81586d24d248..325e1dd3540b 100644 --- a/include/linux/nodemask.h +++ b/include/linux/nodemask.h @@ -488,21 +488,9 @@ static __always_inline int num_node_state(enum node_st= ates state) static __always_inline int node_random(const nodemask_t *maskp) { #if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1) - int w, bit; - - w =3D nodes_weight(*maskp); - switch (w) { - case 0: - bit =3D NUMA_NO_NODE; - break; - case 1: - bit =3D first_node(*maskp); - break; - default: - bit =3D find_nth_bit(maskp->bits, MAX_NUMNODES, get_random_u32_below(w)); - break; - } - return bit; + int node =3D find_random_bit(maskp->bits, MAX_NUMNODES); + + return node < MAX_NUMNODES ? node : NUMA_NO_NODE; #else return 0; #endif diff --git a/lib/find_bit.c b/lib/find_bit.c index 06b6342aa3ae..d4b5a29e3e72 100644 --- a/lib/find_bit.c +++ b/lib/find_bit.c @@ -18,6 +18,7 @@ #include #include #include +#include =20 /* * Common helper for find_bit() function family @@ -291,3 +292,26 @@ EXPORT_SYMBOL(_find_next_bit_le); #endif =20 #endif /* __BIG_ENDIAN */ + +/** + * find_random_bit - find a set bit at random position + * @addr: The address to base the search on + * @size: The bitmap size in bits + * + * Returns: a position of a random set bit; >=3D @size otherwise + */ +unsigned long find_random_bit(const unsigned long *addr, unsigned long siz= e) +{ + int w =3D bitmap_weight(addr, size); + + switch (w) { + case 0: + return size; + case 1: + /* Performance trick for single-bit bitmaps */ + return find_first_bit(addr, size); + default: + return find_nth_bit(addr, size, get_random_u32_below(w)); + } +} +EXPORT_SYMBOL(find_random_bit); --=20 2.43.0