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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA6BBCD54A7 for ; Tue, 19 Sep 2023 08:14:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230364AbjISIOG (ORCPT ); Tue, 19 Sep 2023 04:14:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230376AbjISINu (ORCPT ); Tue, 19 Sep 2023 04:13:50 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CF3CFFB for ; Tue, 19 Sep 2023 01:13:42 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1695111220; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vMN7mNtgI6/V9AqGcVuDSuGP8F5czBGCJW3I64yqozc=; b=udo0Fkd8NNGs9Ba5V4C03Mz61u+jZd6WLTmPE4sKd5SjTxJVoOW4hTt1T3Je9HXNba8UUu t6tC4BHV+yNLHL2wiQGoC5K0CMPupRZ6bOOaUoTYGCPNAXPpnz61e96XFFkfMefPAOIffb kirOgsiPGEyolM/4aP8G7J6OH1gLyx3RUVFJ6fIeE4Q4T/wv0SJwGhtYgR47VqgMCoS4yL 2yJ3dAXzLmX/F/79DI0JSIDK0KcUMcr8CGiRCcwrWvuYySJCqN8zmHSZVyJ6xmAYcPl+Mn UqeKfyIPEopug8UFGX+MktNm9inqAK/LoyGepIMjxdTgGocz2RgRgUS+UWDUAA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1695111220; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vMN7mNtgI6/V9AqGcVuDSuGP8F5czBGCJW3I64yqozc=; b=C3HRybh7lrPRO/xAahoa5tBYRsZHMBB1FgzCS2xefTq6J9rA1O3URcnAFu1JNn4WbQSzww YgyvCCa5DsT9jwCQ== To: K Prateek Nayak , Arjan van de Ven , Peter Zijlstra Cc: LKML , x86@kernel.org, Tom Lendacky , Andrew Cooper , Huang Rui , Juergen Gross , Dimitri Sivanich , Michael Kelley , Wei Liu , Pu Wen , Qiuxu Zhuo , Sohil Mehta , Gautham Shenoy Subject: Re: [patch V4 24/41] x86/cpu: Provide cpu_init/parse_topology() In-Reply-To: <106c0cef-2cde-7330-7a18-31db92c5b04a@amd.com> References: <20230814085006.593997112@linutronix.de> <20230814085113.471353147@linutronix.de> <934072fe-eca2-44df-94e7-9fed1dc8b502@amd.com> <87r0nn8ots.ffs@tglx> <4a4d5a89-b024-ea49-8740-1f3aef412c15@amd.com> <6f101718-7ee1-1c3d-3e0a-3aa708928ecd@amd.com> <20230915115428.GD6721@noisy.programming.kicks-ass.net> <9ffe31b0-a6ff-991d-85ad-97306abfc684@linux.intel.com> <106c0cef-2cde-7330-7a18-31db92c5b04a@amd.com> Date: Tue, 19 Sep 2023 10:13:39 +0200 Message-ID: <87y1h2wpfw.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 19 2023 at 09:24, K Prateek Nayak wrote: > If possible, can you please elaborate on the "software perspective". Say > CPUID leaf 0x1f reports multiple tile, would the data access latency or > cache to cache latency see a noticeable difference? > > I would like to understand what the characteristics of a "Tile" are and > whether they are similar to AMD's CCX instances discoverable by AMD's > extended CPUID leaf 0x80000026. That way, in future, when the generic > topology is used by other subsystems, the data from "TOPO_TILE_DOMAIN" > can be used generically for both Intel and AMD. I'm not convinced that this is possible. The meaning of these elements is unfortunately not cast in stone, so the association of e.g. cache boundaries is not necessarily static accross a larger range of CPU generations.. We really need to differentiate performance characteristic, hardware feature scope, power management scope etc. and create abstractions which are actually useful for kernel facilities and user space. >From a performance perspective it's irrelevant whether the scope is TILE or whatever. The information needed is the hierarchy, the performance characteristics of a segment in the hierarchy and the costs for cross segment access and cross segment migration. For hardware features like perf the information needed is what the scope of a particular resource is. Again it's not necessarily useful to know what particular domain type it is. Powermanagement does not care about the particual type either. It needs to know which scopes affect c-states, clock speeds ... to give the scheduler informtion of how to steer workloads in the most efficient way. Thanks, tglx