From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:39520) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sc2mX-0002l7-A1 for qemu-devel@nongnu.org; Tue, 05 Jun 2012 19:03:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Sc2mV-0008Cb-Ig for qemu-devel@nongnu.org; Tue, 05 Jun 2012 19:03:20 -0400 Received: from mail-pb0-f45.google.com ([209.85.160.45]:37470) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sc2mV-0008CD-CX for qemu-devel@nongnu.org; Tue, 05 Jun 2012 19:03:19 -0400 Received: by pbbro12 with SMTP id ro12so8770839pbb.4 for ; Tue, 05 Jun 2012 16:03:17 -0700 (PDT) Message-ID: <4FCE902A.3060603@codemonkey.ws> Date: Wed, 06 Jun 2012 07:03:06 +0800 From: Anthony Liguori MIME-Version: 1.0 References: <20120605104954.15442.62695.stgit@ltc189.sdl.hitachi.co.jp> <20120605130117.15479.32680.stgit@ltc189.sdl.hitachi.co.jp> <20120605131031.GF13495@aftab.osrc.amd.com> In-Reply-To: <20120605131031.GF13495@aftab.osrc.amd.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH 1/2] ivring: Add a ring-buffer driver on IVShmem List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Borislav Petkov Cc: Ohad Ben-Cohen , Arnaldo Carvalho de Melo , Borislav Petkov , Greg Kroah-Hartman , Yoshihiro YUNOMAE , Rusty Russell , qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, Grant Likely , MyungJoo Ham , Akihiro Nagai , systemtap@sourceware.org, Joerg Roedel , Masami Hiramatsu , yrl.pp-manager.tt@hitachi.com, Cam Macdonell , Linus Walleij On 06/05/2012 09:10 PM, Borislav Petkov wrote: > On Tue, Jun 05, 2012 at 10:01:17PM +0900, Yoshihiro YUNOMAE wrote: >> This patch adds a ring-buffer driver for IVShmem device, a virtual RAM device in >> QEMU. This driver can be used as a ring-buffer for kernel logging or tracing of >> a guest OS by recording kernel programing or SystemTap. >> >> This ring-buffer driver is implemented very simple. First 4kB of shared memory >> region is control structure of a ring-buffer. In this region, some values for >> managing the ring-buffer is stored such as bits and mask of whole memory size, >> writing position, threshold value for notification to a reader on a host OS. >> This region is used by the reader to know writing position. Then, "total >> memory size - 4kB" equals to usable memory region for recording data. >> This ring-buffer driver records any data from start to end of the writable >> memory region. >> >> When writing size exceeds a threshold value, this driver can notify a reader >> to read data by using writel(). As this later patch, reader does not have any >> function for receiving the notification. This notification feature will be used >> near the future. >> >> As a writer records data in this ring-buffer, spinlock function is used to >> avoid competing by some writers in multi CPU environment. Not to use spinlock, >> lockless ring-buffer like as ftrace and one ring-buffer one CPU will be >> implemented near the future. > > Yet another ring buffer? > > We already have an ftrace and perf ring buffer, can't you use one of those? Not to mention virtio :-) Why not just make a virtio device for this kind of thing? Regards, Anthony Liguori >