From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: Implement 3-level event channel routines in Linux. Date: Fri, 4 Jan 2013 11:36:35 -0500 Message-ID: <20130104163635.GB5041@phenom.dumpdata.com> References: <1356979137-18484-1-git-send-email-wei.liu2@citrix.com> <20130102182618.GA13501@phenom.dumpdata.com> <1357152418.8077.75.camel@iceland> <20130102211203.GA15122@phenom.dumpdata.com> <1357214965.18503.11.camel@iceland> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1357214965.18503.11.camel@iceland> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Wei Liu Cc: "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On Thu, Jan 03, 2013 at 12:09:25PM +0000, Wei Liu wrote: > On Wed, 2013-01-02 at 21:12 +0000, Konrad Rzeszutek Wilk wrote: > > On Wed, Jan 02, 2013 at 06:46:58PM +0000, Wei Liu wrote: > > > On Wed, 2013-01-02 at 18:26 +0000, Konrad Rzeszutek Wilk wrote: > > > > On Mon, Dec 31, 2012 at 06:38:54PM +0000, Wei Liu wrote: > > > > > This patch series implements 3-level event channel routines in Linux kernel. > > > > > > > > > > My thought is that 3-level event channel is only useful for Dom0 or driver > > > > > domain, so it is not enabled by default. Enable it with evtchn_level=3 in > > > > > kernel command line. > > > > > > > > Could it be enabled dynamically? Say when we are close to exhausting the > > > > amount of channels? Or if the machine has some large amount of memory and > > > > hence would probably allocate many many guests? > > > > > > > > > > Do you mean enabling this mechanism on the fly when Dom0 / driver domain > > > is running? Or do you mean enabling it based on some metrics when > > > starting up a domain? > > > > Either one. > > > > > > If it is the first case, who is responsible for initiating the switching > > > process? It looks like it is Xen's responsibility to do the switch > > > because Dom0 sometimes cannot know the true capability of underlying > > > hardware. If it is Xen, then we need to add callback to poke Dom0 / > > > driver domain. > > > > Huh? It would be as simple as Dom0 just figuring out that it is > > at the end of the available events (b/c its close to the MAX) and > > then transitioning to the 3-level one (if it can). > > > > We need to manipulate various data structures. IMHO this makes > implementation tricky and racy. > > > > > > > For both cases, what do you have in mind for the metric that used to > > > trigger the switch? How much RAM / how many CPUs is the threshold? > > > > No idea. At what point are we running out of the events? > > In practice, if you have hundreds or thousands of guests running you're > likely of running out of event channels. I presume host capable of doing > this has lots of RAM and CPUs... OK. So "lots" is more than 64GB and 16 CPUS? > > > Wei. >