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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 BAB18C433ED for ; Thu, 20 May 2021 21:41:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 973C66135A for ; Thu, 20 May 2021 21:41:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230301AbhETVmg (ORCPT ); Thu, 20 May 2021 17:42:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41032 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230244AbhETVmf (ORCPT ); Thu, 20 May 2021 17:42:35 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 84DEDC061574; Thu, 20 May 2021 14:41:13 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1621546870; 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=wW24DYlPkr7pkQEBZ+G/csAqmXvvJc049o7EdOTc3zo=; b=xRH/tK+52B87Eo7tPeRpYoYXWeciTZlh3DrLShYY6C/r7eRkNbhXgC3E87qFFxreJ+aWzF rglswI+ZNypjQW/nKyPY4U9en/I1zCYrlY3NCanNtMeqLTmAmZOK3locY19d19ClxPZgHu nrn80/1udqRFZqo2RR/L7hynJcsKJR8DQkAf5gNKrQ4ghXfFQkKKmliHSQ4xoh+t2EHrnn PlpyNiyDO8m0sc3x2Tc3H5+OhXucTJ2ohfGDYZWgNymONVKHwrNLymfYbcyjENDKaJ8erH rYPCXBQZ13pQICaHdy0pHWj6NTNFra8CD02Con9mhZuKlkM4bM98+F7hTPmFOA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1621546870; 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=wW24DYlPkr7pkQEBZ+G/csAqmXvvJc049o7EdOTc3zo=; b=PUh5AoPcGtdQLFK71CDr1AwyPujneKlpGAe6G+Onzh4cRGB/p+/eOXwPvVioU/1JzKlzEM Bo8COlGOrVrd70BQ== To: Len Brown Cc: Borislav Petkov , Willy Tarreau , Andy Lutomirski , Florian Weimer , "Bae\, Chang Seok" , Dave Hansen , X86 ML , LKML , Linux API , "libc-alpha\@sourceware.org" , Rich Felker , Kyle Huey , Keno Fischer , Arjan van de Ven Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features In-Reply-To: References: <20210415044258.GA6318@zn.tnic> <20210415052938.GA2325@1wt.eu> <20210415054713.GB6318@zn.tnic> <20210419141454.GE9093@zn.tnic> <20210419191539.GH9093@zn.tnic> <20210419215809.GJ9093@zn.tnic> <874kf11yoz.ffs@nanos.tec.linutronix.de> <87k0ntazyn.ffs@nanos.tec.linutronix.de> Date: Thu, 20 May 2021 23:41:10 +0200 Message-ID: <87h7ixaxs9.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Len, On Thu, May 20 2021 at 17:22, Len Brown wrote: > On Thu, May 20, 2021 at 4:54 PM Thomas Gleixner wrote: >> > AMX is analogous to the multiplier used by AVX-512. >> > The architectural state must exist on every CPU, including HT siblings. >> > Today, the HT siblings share the same execution unit, >> > and I have no reason to expect that will change. >> >> I'm well aware that HT siblings share the same execution unit for >> AVX. >> >> Though AMX is if I remember the discussions two years ago correctly >> shared by more than the HT siblings which makes things worse. > > I regret that we were unable to get together in the last year to have > an updated discussion. I think if we had, then we would have saved > a lot of mis-understanding and a lot of email! > > So let me emphasize here: > > There is one TMUL execution unit per core. > It is shared by the HT siblings within that core. > > So the comparison to the AVX-512 multiplier is a good one. Fine, but that does not at all change the facts that: 1) It's shared between logical CPUs 2) It has effects on power/thermal and therefore effects which reach outside of the core scope 3) Your appproach of making it unconditionlly available via the proposed #NM prevents the OS and subsequently the system admin / system designer to implement fine grained control over that resource. And no, an opt-in approach by providing a non-mandatory preallocation prctl does not solve that problem. Thanks, tglx