From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2615C64E7B for ; Mon, 30 Nov 2020 17:08:52 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C55B32073C for ; Mon, 30 Nov 2020 17:08:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C55B32073C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=bwidawsk.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46670 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kjmfS-0006WL-JS for qemu-devel@archiver.kernel.org; Mon, 30 Nov 2020 12:08:50 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41294) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kjmeJ-0005Sy-K0 for qemu-devel@nongnu.org; Mon, 30 Nov 2020 12:07:39 -0500 Received: from zangief.bwidawsk.net ([107.170.211.233]:36424 helo=mail.bwidawsk.net) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kjmeH-0007qP-Ul for qemu-devel@nongnu.org; Mon, 30 Nov 2020 12:07:39 -0500 Received: by mail.bwidawsk.net (Postfix, from userid 5001) id 8820E122C68; Mon, 30 Nov 2020 09:07:35 -0800 (PST) Received: from mail.bwidawsk.net (c-73-37-61-164.hsd1.or.comcast.net [73.37.61.164]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by mail.bwidawsk.net (Postfix) with ESMTPSA id 060F3122C3F; Mon, 30 Nov 2020 09:07:31 -0800 (PST) Date: Mon, 30 Nov 2020 09:07:30 -0800 From: Ben Widawsky To: Markus Armbruster Subject: Re: [RFC PATCH 18/25] hw/cxl/device: Add a memory device (8.2.8.5) Message-ID: <20201130170730.o5fkrpaubwcroz4y@mail.bwidawsk.net> References: <20201111054724.794888-1-ben.widawsky@intel.com> <20201111054724.794888-19-ben.widawsky@intel.com> <87d00hk89c.fsf@dusky.pond.sub.org> <20201125165333.zn5tpwfjnwmjmcdu@intel.com> <87360w39qw.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87360w39qw.fsf@dusky.pond.sub.org> Received-SPF: none client-ip=107.170.211.233; envelope-from=ben@bwidawsk.net; helo=mail.bwidawsk.net X-Spam_score_int: -14 X-Spam_score: -1.5 X-Spam_bar: - X-Spam_report: (-1.5 / 5.0 requ) BAYES_00=-1.9, KHOP_HELO_FCRDNS=0.398, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , "Michael S. Tsirkin" , Vishal Verma , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Paolo Bonzini , Igor Mammedov , Dan Williams , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 20-11-26 07:36:23, Markus Armbruster wrote: > Ben Widawsky writes: > > > On 20-11-13 08:47:59, Markus Armbruster wrote: > >> Eric Blake writes: > >> > >> > On 11/10/20 11:47 PM, Ben Widawsky wrote: > >> >> A CXL memory device (AKA Type 3) is a CXL component that contains some > >> >> combination of volatile and persistent memory. It also implements the > >> >> previously defined mailbox interface as well as the memory device > >> >> firmware interface. > >> >> > >> >> The following example will create a 256M device in a 512M window: > >> >> > >> >> -object "memory-backend-file,id=cxl-mem1,share,mem-path=cxl-type3,size=512M" > >> >> -device "cxl-type3,bus=rp0,memdev=cxl-mem1,id=cxl-pmem0,size=256M" > >> >> > >> >> Signed-off-by: Ben Widawsky > >> >> --- > >> > > >> >> +++ b/qapi/machine.json > >> >> @@ -1394,6 +1394,7 @@ > >> >> { 'union': 'MemoryDeviceInfo', > >> >> 'data': { 'dimm': 'PCDIMMDeviceInfo', > >> >> 'nvdimm': 'PCDIMMDeviceInfo', > >> >> + 'cxl': 'PCDIMMDeviceInfo', > >> >> 'virtio-pmem': 'VirtioPMEMDeviceInfo', > >> >> 'virtio-mem': 'VirtioMEMDeviceInfo' > >> >> } > >> > > >> > Missing documentation of the new data type, and the fact that it will be > >> > introduced in 6.0. > >> > >> Old wish list item: improve the QAPI schema frontend to flag this. > >> > > > > "Introduced in 6.0" - quite the optimist. Kidding aside, this is the area where > > I could use some feedback. CXL Type 3 memory devices can contain both volatile > > and persistent memory at the same time. As such, I think I'll need a new type to > > represent that, but I'd love to know how best to accomplish that. > > We can help. Tell us what information you want to provide in variant > 'cxl'. If it's a superset of an existing variant, give us just the > delta. > I'm not exactly sure what the best way to do this is in QEMU, so I'm not really sure what to specify as the delta. A CXL memory device can have both volatile and persistent memory. Currently when a CXL memory device implements the TYPE_MEMORY_DEVICE interface. So I believe the shortest path is a MemoryDeviceInfo that can have two memory devices associated with it, but I don't know if that's the best path. > >> > Also, Markus has been trying to get rid of so-called > >> > "simple unions" in favor of "flat unions" - every time we modify an > >> > existing simple union, it is worth asking if it is time to first flatten > >> > this. > >> > >> 0. Simple unions can be transformed into flat unions. The > >> transformation can either preserve the nested wire format, or flatten > >> it. See docs/devel/qapi-code-gen.txt "A simple union can always be > >> re-written as a flat union ..." > >> > >> 1. No new simple unions. > >> > >> 2. Existing simple unions that can be flattened without breaking > >> backward compatibility have long been flattened. > >> > >> 3. The remaining simple unions are part of QMP, where we need to > >> preserve the wire format. We could turn them into flat union preserving > >> the wire format. Only worthwhile if we kill simple unions and simplify > >> scripts/qapi/. Opportunity to make the flat union syntax less > >> cumbersome. Not done due to lack of time. > >> > >> 4. Kevin and I have been experimenting with ways to provide both flat > >> and nested wire format. This would pave the way for orderly deprecation > >> of the nested wire format. May not be practical for QMP output. > >> > > > > So is there anything for me to do here? > > No. Extending an existing simple union is okay. > > We should not add news ones. We should think twice before we add new > uses of existing ones. > >