From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37283) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fQdlH-0005hD-41 for qemu-devel@nongnu.org; Wed, 06 Jun 2018 15:06:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fQdlF-0007Pk-Pv for qemu-devel@nongnu.org; Wed, 06 Jun 2018 15:06:23 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:37284 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fQdlF-0007PW-KD for qemu-devel@nongnu.org; Wed, 06 Jun 2018 15:06:21 -0400 Date: Wed, 6 Jun 2018 22:06:17 +0300 From: "Michael S. Tsirkin" Message-ID: <20180606220501-mutt-send-email-mst@kernel.org> References: <20180521163203.26590-4-ross.zwisler@linux.intel.com> <20180605182243-mutt-send-email-mst@kernel.org> <20180605164205.GA21034@linux.intel.com> <20180605213547-mutt-send-email-mst@kernel.org> <20180605220700.GB16066@linux.intel.com> <20180606165051.GC30568@linux.intel.com> <20180606170033.GA29035@linux.intel.com> <20180606170849.GA31789@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180606170849.GA31789@linux.intel.com> Subject: Re: [Qemu-devel] [qemu PATCH v4 3/4] nvdimm, acpi: support NFIT platform capabilities List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ross Zwisler Cc: Dan Williams , Eduardo Habkost , linux-nvdimm , Qemu Developers , Stefan Hajnoczi , Igor Mammedov On Wed, Jun 06, 2018 at 11:08:49AM -0600, Ross Zwisler wrote: > On Wed, Jun 06, 2018 at 11:00:33AM -0600, Ross Zwisler wrote: > > On Wed, Jun 06, 2018 at 10:50:51AM -0600, Ross Zwisler wrote: > > > On Tue, Jun 05, 2018 at 03:21:30PM -0700, Dan Williams wrote: > > > > On Tue, Jun 5, 2018 at 3:07 PM, Ross Zwisler > > > > wrote: > > > > > On Tue, Jun 05, 2018 at 09:37:25PM +0300, Michael S. Tsirkin wrote: > > > > >> On Tue, Jun 05, 2018 at 11:15:00AM -0700, Dan Williams wrote: > > > > >> > On Tue, Jun 5, 2018 at 9:42 AM, Ross Zwisler > > > > >> > wrote: > > > > >> > > On Tue, Jun 05, 2018 at 06:25:27PM +0300, Michael S. Tsirkin wrote: > > > > >> > >> On Mon, May 21, 2018 at 10:32:02AM -0600, Ross Zwisler wrote: > > > > >> > >> > Add a machine command line option to allow the user to control the Platform > > > > >> > >> > Capabilities Structure in the virtualized NFIT. This Platform Capabilities > > > > >> > >> > Structure was added in ACPI 6.2 Errata A. > > > > >> > >> > > > > > >> > >> > Signed-off-by: Ross Zwisler > > > > >> > >> > > > > >> > >> I tried playing with it and encoding the capabilities is > > > > >> > >> quite awkward. > > > > >> > >> > > > > >> > >> Can we add bits for specific capabilities instead of nvdimm-cap? > > > > >> > >> > > > > >> > >> How about: > > > > >> > >> > > > > >> > >> "cpu-flush-on-power-loss-cap" > > > > >> > >> "memory-flush-on-power-loss-cap" > > > > >> > >> "byte-addressable-mirroring-cap" > > > > >> > > > > > > >> > > Hmmm...I don't like that as much because: > > > > >> > > > > > > >> > > a) It's very verbose. Looking at my current qemu command line few other > > > > >> > > options require that many characters, and you'd commonly be defining more > > > > >> > > than one of these for a given VM. > > > > >> > > > > > > >> > > b) It means that the QEMU will need to be updated if/when new flags are added, > > > > >> > > because we'll have to have new options for each flag. The current > > > > >> > > implementation is more future-proof because you can specify any flags > > > > >> > > value you want. > > > > >> > > > > > > >> > > However, if you feel strongly about this, I'll make the change. > > > > >> > > > > > >> > Straw-man: Could we do something similar with what we are doing in ndctl? > > > > >> > > > > > >> > enum ndctl_persistence_domain { > > > > >> > PERSISTENCE_NONE = 0, > > > > >> > PERSISTENCE_MEM_CTRL = 10, > > > > >> > PERSISTENCE_CPU_CACHE = 20, > > > > >> > PERSISTENCE_UNKNOWN = INT_MAX, > > > > >> > }; > > > > >> > > > > > >> > ...and have the command line take a number where "10" and "20" are > > > > >> > supported today, but allows us to adapt to new persistence domains in > > > > >> > the future. > > > > >> > > > > >> I'm fine with that except can we have symbolic names instead of numbers > > > > >> on command line? > > > > >> > > > > >> -- > > > > >> MST > > > > > > > > > > Okay, we can move to the symbolic names. Do you want them to be that long, or > > > > > would: > > > > > > > > > > nvdimm-cap-cpu > > > > > nvdimm-cap-mem-ctrl > > > > > nvdimm-cap-mirroring > > > > > > > > Wait, why is mirroring part of this? > > > > > > > > I was thinking this option would be: > > > > > > > > --persistence-domain={cpu,mem-ctrl} > > > > > > > > ...and try not to let ACPI specifics leak into the qemu command line > > > > interface. For example PowerPC qemu could have a persistence domain > > > > communicated via Open Firmware or some other mechanism. > > > > > > Sure, this seems fine, though we may want to throw an "nvdimm" in the name > > > somewhere so it's clear what the option affects. > > > > > > nvdimm-persistence={cpu,mem-ctrl} maybe? > > > > > > Michael, does this work for you? > > > > Hmm...also, the version of these patches that used numeric values did go > > upstream in QEMU. So, do we need to leave that interface intact, and just add > > a new one that uses symbolic names? Or did you still just want to replace the > > numeric one since it hasn't appeared in a QEMU release yet? > > I guess another alternative would be to just add symbolic name options to the > existing command line option, i.e. allow all of these: > > nvdimm-cap=3 # CPU cache > nvdimm-cap=cpu # CPU cache > nvdimm-cap=2 # memory controller > nvdimm-cap=mem-ctrl # memory controller > > And just have them as aliases. This retains backwards compatibility with > what is already there, allows for other numeric values without QEMU updates if > other bits are defined (though we are still tightly tied to ACPI in this > case), and provides a symbolic name which is easier to use. > > Thoughts? I'm inclined to say let's just keep the symbolic names. Less of a chance users configure something incorrectly, it somehow kind of works and then we get stuck with working around these bugs. -- MST