From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by sourceware.org (Postfix) with ESMTPS id 9380A3858024 for ; Fri, 26 Mar 2021 10:08:35 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 9380A3858024 Received: from zn.tnic (p4fed36c1.dip0.t-ipconnect.de [79.237.54.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 00A871EC0516; Fri, 26 Mar 2021 11:08:33 +0100 (CET) Date: Fri, 26 Mar 2021 11:06:20 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: libc-alpha , "H. J. Lu" , X86 ML , LKML , "Bae, Chang Seok" , Florian Weimer , Carlos O'Donell , Rich Felker Subject: Re: Why does glibc use AVX-512? Message-ID: <20210326100620.GA25229@zn.tnic> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-5.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 26 Mar 2021 10:08:38 -0000 On Thu, Mar 25, 2021 at 09:38:24PM -0700, Andy Lutomirski wrote: > I think we should seriously consider solutions in which, for new > tasks, XCR0 has new giant features (e.g. AMX) and possibly even > AVX-512 cleared, and programs need to explicitly request enablement. I totally agree with making this depend on an explicit user request, but... > This would allow programs to opt into not saving/restoring across > signals or to save/restore in buffers supplied when the feature is > enabled. This has all kinds of pros and cons, and I'm not sure it's a > great idea. But, in the absence of some change to the ABI, the > default outcome is that, on AMX-enabled kernels on AMX-enabled > hardware, the signal frame will be more than 8kB, and this will affect > *every* signal regardless of whether AMX is in use. ... what's stopping the library from issuing that new ABI call before it starts the app and get automatically enabled for everything by default? And then we'll get the lazy FPU thing all over again. So the ABI should be explicit user interaction or a kernel cmdline param or so. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette