From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Thornber Subject: Re: [dm-devel] Questions about the function, queue_empty in dm-cache-policy-mq.c Date: Mon, 5 Jan 2015 09:17:08 +0000 Message-ID: <20150105091707.GA11818@debian> References: <54AA03E0.9020900@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <54AA03E0.9020900@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: device-mapper development Cc: agk@redhat.com, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, snitzer@redhat.com List-Id: linux-raid.ids 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