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 8C18BC761A6 for ; Thu, 6 Apr 2023 13:17:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237551AbjDFNRr (ORCPT ); Thu, 6 Apr 2023 09:17:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43668 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229817AbjDFNRq (ORCPT ); Thu, 6 Apr 2023 09:17:46 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B86159F9 for ; Thu, 6 Apr 2023 06:17:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680787020; 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=rEZb6SaUsngmnCMPg4YGowc9TbgaZEBXr+mRqfM4dbw=; b=L9bvvX0HUgj5Ia4Sdazsh7hYJdQ7NjenSVL2IEAavelW4pO6fF8Bapm3+mqjmPKExqhCOS 1PMoofur1pZCogD3rEJUr9OCLY465Xx2RejyHj6TruoXRsCtsS3Zq74abVpau5BqYSjf4a Fut0ai/sTJeD8VnDz9aA9b8QxVq7ca0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-643-10l_5oWZPX2YbGgfWqkGXw-1; Thu, 06 Apr 2023 09:16:57 -0400 X-MC-Unique: 10l_5oWZPX2YbGgfWqkGXw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2B0A9884EC0; Thu, 6 Apr 2023 13:16:55 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 82F2D2166B26; Thu, 6 Apr 2023 13:16:54 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id A64FC40EB07D7; Thu, 6 Apr 2023 09:49:22 -0300 (-03) Date: Thu, 6 Apr 2023 09:49:22 -0300 From: Marcelo Tosatti To: Peter Zijlstra 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: References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> <20230405195457.GC365912@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230405195457.GC365912@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Wed, Apr 05, 2023 at 09:54:57PM +0200, Peter Zijlstra wrote: > 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? Yes, IPIs to vCPU (guest context). In this case we can consider an IPI to the host pCPU (which requires VM-exit from guest context). > 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. I suppose its common practice to use certain system calls in latency sensitive applications, for example nanosleep. Some examples: 1) cyclictest (nanosleep) 2) PLC programs (nanosleep) A system call does not necessarily have to take locks, does it ? Or even if application does system calls, but runs under a VM, then you are requiring it to never VM-exit. This reduces the flexibility of developing such applications. 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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2795EC76196 for ; Thu, 6 Apr 2023 13:18:49 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4PshsM3dYxz3fSB for ; Thu, 6 Apr 2023 23:18:47 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=ZfVeh5HW; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=Efid/otI; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; 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Thu, 6 Apr 2023 13:16:55 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 82F2D2166B26; Thu, 6 Apr 2023 13:16:54 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id A64FC40EB07D7; Thu, 6 Apr 2023 09:49:22 -0300 (-03) Date: Thu, 6 Apr 2023 09:49:22 -0300 From: Marcelo Tosatti To: Peter Zijlstra Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Message-ID: References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> <20230405195457.GC365912@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230405195457.GC365912@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, dave.hansen@linux.intel.com, Yair Podemsky , sebastian.reichel@collabora.com, linux-mm@kvack.org, hpa@zytor.com, sparclinux@vger.kernel.org, agordeev@linux.ibm.com, will@kernel.org, ardb@kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, vschneid@redhat.com, arnd@arndb.de, paulmck@kernel.org, aneesh.kumar@linux.ibm.com, x86@kernel.org, linux@armlinux.org.uk, mingo@redhat.com, samitolvanen@google.com, borntraeger@linux.ibm.com, hca@linux.ibm.com, keescook@chromium.org, gor@linux.ibm.com, Frederic Weisbecker , npiggin@gmail.com, rmk+kernel@armlinux.org.uk, bp@alien8.de, nick.hawkins@hpe.com, tglx@linutronix.de, jpoimboe@kernel.org, linux-arm-kernel@lists.infradead.org, alougovs@redhat.com, linux-kernel@vger.kernel.org, juerg.haefliger@canonical.com, svens@linux.ibm.com, dhildenb@redhat.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, davem@da vemloft.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Apr 05, 2023 at 09:54:57PM +0200, Peter Zijlstra wrote: > 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? Yes, IPIs to vCPU (guest context). In this case we can consider an IPI to the host pCPU (which requires VM-exit from guest context). > 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. I suppose its common practice to use certain system calls in latency sensitive applications, for example nanosleep. Some examples: 1) cyclictest (nanosleep) 2) PLC programs (nanosleep) A system call does not necessarily have to take locks, does it ? Or even if application does system calls, but runs under a VM, then you are requiring it to never VM-exit. This reduces the flexibility of developing such applications. 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Thu, 06 Apr 2023 09:16:57 -0400 X-MC-Unique: 10l_5oWZPX2YbGgfWqkGXw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2B0A9884EC0; Thu, 6 Apr 2023 13:16:55 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 82F2D2166B26; Thu, 6 Apr 2023 13:16:54 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id A64FC40EB07D7; Thu, 6 Apr 2023 09:49:22 -0300 (-03) Date: Thu, 6 Apr 2023 09:49:22 -0300 From: Marcelo Tosatti To: Peter Zijlstra 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: References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> <20230405195457.GC365912@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230405195457.GC365912@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230406_061707_278606_18303666 X-CRM114-Status: GOOD ( 23.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Apr 05, 2023 at 09:54:57PM +0200, Peter Zijlstra wrote: > 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? Yes, IPIs to vCPU (guest context). In this case we can consider an IPI to the host pCPU (which requires VM-exit from guest context). > 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. I suppose its common practice to use certain system calls in latency sensitive applications, for example nanosleep. Some examples: 1) cyclictest (nanosleep) 2) PLC programs (nanosleep) A system call does not necessarily have to take locks, does it ? Or even if application does system calls, but runs under a VM, then you are requiring it to never VM-exit. This reduces the flexibility of developing such applications. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel