From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753546AbbAEJRa (ORCPT ); Mon, 5 Jan 2015 04:17:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51993 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753333AbbAEJRK (ORCPT ); Mon, 5 Jan 2015 04:17:10 -0500 Date: Mon, 5 Jan 2015 09:17:08 +0000 From: Joe Thornber To: device-mapper development Cc: agk@redhat.com, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, snitzer@redhat.com Subject: Re: [dm-devel] Questions about the function, queue_empty in dm-cache-policy-mq.c Message-ID: <20150105091707.GA11818@debian> Mail-Followup-To: device-mapper development , agk@redhat.com, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, snitzer@redhat.com References: <54AA03E0.9020900@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54AA03E0.9020900@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 04, 2015 at 10:24:16PM -0500, nick wrote: > Greetings All, > I have a few questions about the function I stated in the message for this email. > 1. What is the issues with the CPU usage for this function? At the moment it can perform up to NR_QUEUE_LEVELS (16) list_empty() calls. Which I consider too much work for a function that is called frequently. > 2. What hardware is this on ? Irrelevant. > 3. How scalable is this function in terms of NR_QUEUE_LEVELS and how many does it need to handle? Linear. NR_QUEUE_LEVELS is a compile time constant currently set to 16, and unlikely to change. - Joe