From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (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 1C94913BADF; Tue, 28 Jan 2025 19:10:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738091448; cv=none; b=GkBn3rU/kHFlnLu3eVVOqaUBhrAC+oK8NZ/k/pNgcLx9sAgW8KLM7y8qUObmM8+EYpqkHkzwj8DdVLpf9PdqPC5lhLpn45uaV3Phh68Tc/mOruZOEdzHDzB0HGAM88oOz9KTKzcAl7Th7DwRPqrXNA2NpndAXuLNecCqj8MauFU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738091448; c=relaxed/simple; bh=jvVjfJzusy/T2TFETbNIWWcoexj5Y83nv715DHc81ow=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G7bS349KozohkphG40CzPAVyw+siJWoS5uXrLRgJPeKOH5tjyXEcAvHHtk7Y69ASSk8zQcI+b5U2tIBuIIjlaREdSEGCZOlX8pNPUPC3fpFo6izIKh8mIodmqWgNxHHuDj3ihV1v+3pdBlVvY9Wozu0/AGA7rFGoJmRvZXMKaOA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=ab8M+HZ6; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="ab8M+HZ6" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=bbMLXJyynd4nYkMR/7HO4+Jzw6FmMDgG7jfaJOUdBxU=; b=ab8M+HZ6Fn9AEtWNK8cMRzU4wU +LQjbdNX2p5owXiTC3COpG92H077aarRc+F98k223qJ2pMQl++mekh2N0zGEIhuOzV7F1irS0OO3H F9ip2PZ63/8wtaqbHrRBi1YE9HagnXbIHaqpKpotO/mouutbTzn62cJC1J1EL2cJz2FfZ50UvKgf0 S3ww+gTYEIueP/MSpwlY3GaBfC/Eg2zfhUird0WRgZTsFPfDXiZ7ACcceoogRcYrO+R/M9gmGZIVh wmxV8M1V2GPhL5xnCkckO/KT0LuECf8BFyi6rNWi6M+B3BOEtSyyJwCwIwvZ4lV9K18Q8LAHUt64I BkS8SjDA==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.98 #2 (Red Hat Linux)) id 1tcqyw-0000000EWLb-2hCw; Tue, 28 Jan 2025 19:10:42 +0000 Date: Tue, 28 Jan 2025 19:10:42 +0000 From: Al Viro To: Oliver Sang Cc: oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Christian Brauner , linux-fsdevel@vger.kernel.org Subject: Re: [linus:master] [do_pollfd()] 8935989798: will-it-scale.per_process_ops 11.7% regression Message-ID: <20250128191042.GO1977892@ZenIV> References: <202501261509.b6b4260d-lkp@intel.com> <20250127192616.GG1977892@ZenIV> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro On Tue, Jan 28, 2025 at 05:37:39PM +0800, Oliver Sang wrote: > > Just to make sure it's not a geniune change of logics somewhere, > > could you compare d000e073ca2a, 893598979838 and d000e073ca2a with the > > delta below? That delta provably is an equivalent transformation - all > > exits from do_pollfd() go through the return in the end, so that just > > shifts the last assignment in there into the caller. > > the 'd000e073ca2a with the delta below' has just very similar score as > d000e073ca2a as below. Not a change of logics, then... AFAICS, the only differences in code generation here are different spills and conditional fput() not taken out of line. I'm somewhat surprised by the amount of slowdowns, TBH... Is there any chance to get per-insn profiles for those? How much time is spent in each insn of do_poll()/do_pollfd()?