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 E3A89C7619A for ; Wed, 5 Apr 2023 19:56:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233704AbjDET4m (ORCPT ); Wed, 5 Apr 2023 15:56:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233489AbjDET4l (ORCPT ); Wed, 5 Apr 2023 15:56:41 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4EEAC0; Wed, 5 Apr 2023 12:56:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=B30n3pHhQ67VUrCvHblGlQhSttCrPNMRQNjpDfnCSKM=; b=CJI95hU4T3CctR2X2KCz7i8NWi YVt1ex1JpgAHIkmuy1kwgmXIwoo8mBoQM1QWzDBBKhLlgV5gG20QMCPVnsJLgz7GRzOm4rDjqGEX7 SmFG/4YZOLagPlJCfMyKsqXiKz6fWZ/Jk9afJU/jjYA7gG9XdM9XNSnVMS1ZUyvJEx5WQFenjZoAI zO2cSWiVjU2pubWN8bbwjUL6wmrfBNOTp8MuoRZde24eZSrrkyuyRHB2Tk3nQSha1cz0pm0m39FhU k2KMEzOUMhMRj2A+rxwttKpIIRQXafgeaIFhn68NBf9aN8oHHlDlL/YAU/DyPzhJcQlSRGMXoJ0cF xlMCIp8w==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1pk9De-00A4Ht-2h; Wed, 05 Apr 2023 19:54:59 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B6577300194; Wed, 5 Apr 2023 21:54:57 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9929B200B42A8; Wed, 5 Apr 2023 21:54:57 +0200 (CEST) Date: Wed, 5 Apr 2023 21:54:57 +0200 From: Peter Zijlstra To: Marcelo Tosatti Cc: Frederic Weisbecker , Yair Podemsky , linux@armlinux.org.uk, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, will@kernel.org, aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org, arnd@arndb.de, keescook@chromium.org, paulmck@kernel.org, jpoimboe@kernel.org, samitolvanen@google.com, ardb@kernel.org, juerg.haefliger@canonical.com, rmk+kernel@armlinux.org.uk, geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, sebastian.reichel@collabora.com, nick.hawkins@hpe.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, vschneid@redhat.com, dhildenb@redhat.com, alougovs@redhat.com Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Message-ID: <20230405195457.GC365912@hirez.programming.kicks-ass.net> References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Wed, Apr 05, 2023 at 04:43:14PM -0300, Marcelo Tosatti wrote: > Two points: > > 1) For a virtualized system, the overhead is not only of executing the > IPI but: > > VM-exit > run VM-exit code in host > handle IPI > run VM-entry code in host > VM-entry I thought we could do IPIs without VMexit these days? Also virt... /me walks away. > 2) Depends on the application and the definition of "occasional". > > For certain types of applications (for example PLC software or > RAN processing), upon occurrence of an event, it is necessary to > complete a certain task in a maximum amount of time (deadline). If the application is properly NOHZ_FULL and never does a kernel entry, it will never get that IPI. If it is a pile of shit and does kernel entries while it pretends to be NOHZ_FULL it gets to keep the pieces and no amount of crying will get me to care.