From nobody Thu Dec 18 12:59:21 2025 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.17]) (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 76299181323; Fri, 14 Jun 2024 16:08:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.17 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718381336; cv=none; b=FqCXoUSiBf9M+Q0wrEXYS2sfpG50GhDTa4W48DTurcBDPuyKcsURQMIG6Wo7czRw6//YebHkK/ycuN+J9LCzN6LGiHBFktep4B1eiVCSoju+hLgyuuvpGGI1nWUeGCf+ctLI0mANWawOA6Z75GluYu95BHEg986U0xfHLAS6www= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718381336; c=relaxed/simple; bh=PW1CwgwF4DEJPAtCw5E8u2zb9VKV5pgVkPiDLQwmwMg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kRDwojqr4km8qBGEjgG6gCgKqhQN/rgsgqGe3tnwaD/ISLh9XVZinIoQJfcosNyY9Tgj7ZVWW0bUYYMmmLwFS9/mKu/fgBvfiosl9bMorBQ0Kt2epL0qZFhD3BT4LntvVc1sVXKBuM6bvjw2kBjhwgSJasBtGIFB7QdNPW8o8Vo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=KJemTTI4; arc=none smtp.client-ip=198.175.65.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="KJemTTI4" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1718381334; x=1749917334; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=PW1CwgwF4DEJPAtCw5E8u2zb9VKV5pgVkPiDLQwmwMg=; b=KJemTTI48iVgiG+z1cqTsCyZOSKwMmF+owKz8g7Lp7FxJjfr7PUwsgYY Vs6gFTXhIjtjuPqRzgSZYldKayrG4d8KbX7dSTvp8a9xonaVqU1lyy+OC R1Oez9MMFLsVnLZOLNO+dkudMILQwfAsGV1NVuX1DArzuSqAPx3LCjvaM rGBQiE/P8Y+a6YXX7p1Et4cF0Hb7b/Ou51A15ADxlUnaqXdkkkwSmRgoG cN6FW+PTVgbUtRLx+15HT3GZuQhMu7SMZ241Wy21x5Ue/pXUIQFhV4+s5 J/hhxElhvjbVAAnhODvvvNYUBVU7ef9iQ+UeJfJOrJCxKYjvbu3IEewU9 w==; X-CSE-ConnectionGUID: ipZD0eH/RSCv9qktbPlTlQ== X-CSE-MsgGUID: uf3cEddyQHyZOPtJS2A3lg== X-IronPort-AV: E=McAfee;i="6700,10204,11103"; a="15399385" X-IronPort-AV: E=Sophos;i="6.08,238,1712646000"; d="scan'208";a="15399385" Received: from fmviesa001.fm.intel.com ([10.60.135.141]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2024 09:08:54 -0700 X-CSE-ConnectionGUID: yBxsODLRSlK45G+x8PXgMA== X-CSE-MsgGUID: ygVkJ34WQKyUBeRivbolNg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,238,1712646000"; d="scan'208";a="71741074" Received: from linux-pnp-server-16.sh.intel.com ([10.239.177.152]) by fmviesa001.fm.intel.com with ESMTP; 14 Jun 2024 09:08:51 -0700 From: Yu Ma To: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, tim.c.chen@intel.com, pan.deng@intel.com, tianyou.li@intel.com, yu.ma@intel.com Subject: [PATCH 1/3] fs/file.c: add fast path in alloc_fd() Date: Fri, 14 Jun 2024 12:34:14 -0400 Message-ID: <20240614163416.728752-2-yu.ma@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240614163416.728752-1-yu.ma@intel.com> References: <20240614163416.728752-1-yu.ma@intel.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" There is available fd in the lower 64 bits of open_fds bitmap for most cases when we look for an available fd slot. Skip 2-levels searching via find_next_zero_bit() for this common fast path. Look directly for an open bit in the lower 64 bits of open_fds bitmap when a free slot is available there, as: (1) The fd allocation algorithm would always allocate fd from small to larg= e. Lower bits in open_fds bitmap would be used much more frequently than higher bits. (2) After fdt is expanded (the bitmap size doubled for each time of expansi= on), it would never be shrunk. The search size increases but there are few open = fds available here. (3) There is fast path inside of find_next_zero_bit() when size<=3D64 to sp= eed up searching. With the fast path added in alloc_fd() through one-time bitmap searching, pts/blogbench-1.1.0 read is improved by 20% and write by 10% on Intel ICX 1= 60 cores configuration with v6.8-rc6. Reviewed-by: Tim Chen Signed-off-by: Yu Ma --- fs/file.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/file.c b/fs/file.c index 3b683b9101d8..e8d2f9ef7fd1 100644 --- a/fs/file.c +++ b/fs/file.c @@ -510,8 +510,13 @@ static int alloc_fd(unsigned start, unsigned end, unsi= gned flags) if (fd < files->next_fd) fd =3D files->next_fd; =20 - if (fd < fdt->max_fds) + if (fd < fdt->max_fds) { + if (~fdt->open_fds[0]) { + fd =3D find_next_zero_bit(fdt->open_fds, BITS_PER_LONG, fd); + goto success; + } fd =3D find_next_fd(fdt, fd); + } =20 /* * N.B. For clone tasks sharing a files structure, this test @@ -531,7 +536,7 @@ static int alloc_fd(unsigned start, unsigned end, unsig= ned flags) */ if (error) goto repeat; - +success: if (start <=3D files->next_fd) files->next_fd =3D fd + 1; =20 --=20 2.43.0