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Wed, 26 Mar 2025 05:53:16 -0700 (PDT) Date: Wed, 26 Mar 2025 08:53:14 -0400 From: Gregory Price To: Yuquan Wang Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [LSF/MM] CXL Boot to Bash - Section 4: Interleave Message-ID: References: Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Mar 26, 2025 at 05:28:00PM +0800, Yuquan Wang wrote: > > > > Notice at both the root and the host bridge, the Interleave Ways is 2. > > There are two targets at each level. The host bridge has a granularity > > of 512 to capture its parent's ways and granularity (`2*256`). > > > > Each decoder is programmed with the total number of targets (4) and the > > overall granularity (256B). > > > > Sorry, I tried to set this topology on Qemu Virt and used: > "cxl create-region -d decoder0.0 -t ram -m mem0,mem1,mem2,mem3" > > but it failed with: > "cxl region: validate_ways: Interleave ways 2 is less than number of memdevs specified: 4" > > It seems like the CFMWs IW should be 4? > It has been a while since i've interacted with QEMU's interleave stuff, but IIRC (at least back when I was working on it) most configurations had 1 device per host bridge - in which case the CFMWS IW should be 4 with each of the host bridges described in it. I'm not sure you can do multiple devices per host bridge without a switch setup. ~Gregory