From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DB8A5CCF9E0 for ; Fri, 24 Oct 2025 14:06:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=r5JQM8tjVJeTnSP+fubx3nNdoQqoxOINnnSnyg4/w9g=; b=Z5dBQU1uhwsdQmhi8w4j+CD33g QFl51bI2TBg0sVDZn2URy0XSHQeOzKpTBrLbrB4gbWbQUKDB98Rw38f9pObWBOaBoeUY/gpjkMbEj 2zrQoAqqIp75DRcU9gqyAk+CxRSiC5cjMGuugPkhMBp/nKOcBNn6kL/wypifTbrt4afKn7PK8rj/l iAfDSRop8zxouHNdUAzkDSXbYoIMuWe1yTEv7Eedd4dzdHirZNcrZh9126CnpDpPu5wQNMAVaAybJ ucEWw6JpT3AqfiYS6/WljHz6TqaV8TUjG6opqsDQaWTKxOQAXU+xtRRnE5sxVB7WsE3dyHfV4mXE2 zcS67qDA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vCIQV-00000009c58-3fGM; Fri, 24 Oct 2025 14:05:55 +0000 Received: from mgamail.intel.com ([198.175.65.20]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vCIQS-00000009c4W-31XZ; Fri, 24 Oct 2025 14:05:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1761314752; x=1792850752; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=WoimfDSkoiRGXr+VziBQJvHHKgL57NRpG6O9qXGaAE0=; b=JMT1pQam6eiN6VbssX9M49TbKDnTRtn5sNIqONIhYmqU1VtHPM24Wdio d1dGc1cMUMFCOWFI8AW2KlWbKdYndm9jmuu1tx7+0co9igkp438UMcJwE DJ/JVIJalcvFMv3kfIAhjprfMlBYF6Qw+8kHV7gg+X0Dce1QN6aTXY5cT zPDOs+P+uvDfniT9tBJIjvjBytK0RLJFYx5DXF0us0GCNETGpu5oXBvyZ mCE0zc/vbdoY50fsBptGQNX1WtyL2ntvOWD2+63t0gp//eW/58c46mX0X Afv0kreP8MK+7nGxZv++FltcDRdfyX/hwP9j5pUNKwgqmkzGJMrn7LcVZ w==; X-CSE-ConnectionGUID: da03AWznQLioGMU5oLIEzA== X-CSE-MsgGUID: RZlFnRP0TiWaTQxy/ROhCg== X-IronPort-AV: E=McAfee;i="6800,10657,11586"; a="63199488" X-IronPort-AV: E=Sophos;i="6.19,252,1754982000"; d="scan'208";a="63199488" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Oct 2025 07:05:52 -0700 X-CSE-ConnectionGUID: LEfpDIHESSiaqwLNEzO8aQ== X-CSE-MsgGUID: wbSold2QTOiiflfqUdPudA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,252,1754982000"; d="scan'208";a="208083206" Received: from spandruv-desk1.amr.corp.intel.com (HELO [10.125.109.24]) ([10.125.109.24]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Oct 2025 07:05:51 -0700 Message-ID: Date: Fri, 24 Oct 2025 07:05:50 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] epoll: Use __user_write_access_begin() and unsafe_put_user() in epoll_put_uevent(). To: Kuniyuki Iwashima Cc: alex@ghiti.fr, aou@eecs.berkeley.edu, axboe@kernel.dk, bp@alien8.de, brauner@kernel.org, catalin.marinas@arm.com, christophe.leroy@csgroup.eu, dave.hansen@linux.intel.com, edumazet@google.com, hpa@zytor.com, kuni1840@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, maddy@linux.ibm.com, mingo@redhat.com, mpe@ellerman.id.au, npiggin@gmail.com, palmer@dabbelt.com, pjw@kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org, will@kernel.org, x86@kernel.org References: <0bfa4895-727b-407b-90d2-7d54b9bd4910@intel.com> <20251024051653.66329-1-kuniyu@google.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20251024051653.66329-1-kuniyu@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251024_070552_801225_5E2536BE X-CRM114-Status: GOOD ( 11.09 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 10/23/25 22:16, Kuniyuki Iwashima wrote: >> This makes me nervous. The access_ok() check is quite a distance away. >> I'd kinda want to see some performance numbers before doing this. Is >> removing a single access_ok() even measurable? > I noticed I made a typo in commit message, s/tcp_rr/udp_rr/. > > epoll_put_uevent() can be called multiple times in a single > epoll_wait(), and we can see 1.7% more pps on UDP even when > 1 thread has 1000 sockets only: > > server: $ udp_rr --nolog -6 -F 1000 -T 1 -l 3600 > client: $ udp_rr --nolog -6 -F 1000 -T 256 -l 3600 -c -H $SERVER > server: $ nstat > /dev/null; sleep 10; nstat | grep -i udp > > Without patch (2 stac/clac): > Udp6InDatagrams 2205209 0.0 > > With patch (1 stac/clac): > Udp6InDatagrams 2242602 0.0 I'm totally with you about removing a stac/clac: https://lore.kernel.org/lkml/20250228203722.CAEB63AC@davehans-spike.ostc.intel.com/ The thing I'm worried about is having the access_ok() so distant from the unsafe_put_user(). I'm wondering if this: - __user_write_access_begin(uevent, sizeof(*uevent)); + if (!user_write_access_begin(uevent, sizeof(*uevent)) + return NULL; unsafe_put_user(revents, &uevent->events, efault); unsafe_put_user(data, &uevent->data, efault); user_access_end(); is measurably slower than what was in your series. If it is not measurably slower, then the series gets simpler because it does not need to refactor user_write_access_begin(). It also ends up more obviously correct because the access check is closer to the unsafe_put_user() calls. Also, the extra access_ok() is *much* cheaper than stac/clac.