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=-6.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 2A8A2C433E5 for ; Mon, 27 Jul 2020 13:30:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07BAA2074F for ; Mon, 27 Jul 2020 13:30:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="axc+fmSP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728866AbgG0Nae (ORCPT ); Mon, 27 Jul 2020 09:30:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56888 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726320AbgG0Nad (ORCPT ); Mon, 27 Jul 2020 09:30:33 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6B10C061794; Mon, 27 Jul 2020 06:30:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; 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=kyc3BfjwesjA1ByfvEc2/LYx9mR5ZObBawwL9fp0vYM=; b=axc+fmSPwCejjbt6xZSmADYBU5 piPxmkw1iKcFVUI7Sce/EVLU0OwkxXn0yrdjxSILF7qwkLv6pp4e9l04CX1N2CKOjKYBFc1/vCnXJ o0tnjxmUtj7OawPZEfjOZYAmsmfU7aXIteVGGwGSEesu1esWjbF9czKK7WsOebq5xbbou2Eal+b+K B7+ULeiN+KpqCynpiQtv5vI6WNcE1yl7ds0HHvp8w4trerRp/h5baaWCQKbrQejZBdjpb6pipWiiO dUVGpZgJeoaw6n/VGBBOGKmj72uW7T6lJm3O/sT1vT1R1rScZbEcs86+AU6wirdzHTkIiWpX/yAvl 5u01TQEA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k03Cx-0005B4-1L; Mon, 27 Jul 2020 13:30:23 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 0980230018A; Mon, 27 Jul 2020 15:30:21 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DDFED29DBEB19; Mon, 27 Jul 2020 15:30:20 +0200 (CEST) Date: Mon, 27 Jul 2020 15:30:20 +0200 From: peterz@infradead.org To: hpa@zytor.com Cc: Ricardo Neri , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , x86@kernel.org, Dave Hansen , Tony Luck , Cathy Zhang , Fenghua Yu , Kyung Min Park , "Ravi V. Shankar" , Sean Christopherson , linux-kernel@vger.kernel.org, Ricardo Neri , Dave Hansen , linux-edac@vger.kernel.org, frederic@kernel.org Subject: Re: [PATCH 4/4] x86/cpu: Use SERIALIZE in sync_core() when available Message-ID: <20200727133020.GN119549@hirez.programming.kicks-ass.net> References: <20200727043132.15082-1-ricardo.neri-calderon@linux.intel.com> <20200727043132.15082-5-ricardo.neri-calderon@linux.intel.com> <20200727083619.GF119549@hirez.programming.kicks-ass.net> <49251CFA-8AC3-462D-A60F-0337593BE9CD@zytor.com> <20200727130536.GM119549@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200727130536.GM119549@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 27, 2020 at 03:05:36PM +0200, peterz@infradead.org wrote: > Yeah, I'm not sure.. the 'funny' thing is that typically call > sync_core() from an IPI anyway. And the synchronous broadcast IPI is by > far the most expensive part of that. > > Something like this... > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 20e07feb4064..528e049ee1d9 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -989,12 +989,13 @@ void *text_poke_kgdb(void *addr, const void *opcode, size_t len) > > static void do_sync_core(void *info) > { > - sync_core(); > + /* IRET implies sync_core() */ > } > > void text_poke_sync(void) > { > on_each_cpu(do_sync_core, NULL, 1); > + sync_core(); > } > > struct text_poke_loc { So 'people' have wanted to optimize this for NOHZ_FULL and I suppose virt as well. IFF VMENTER is serializing, I suppose we can simply do something like: bool text_poke_cond(int cpu, void *info) { /* * If we observe the vCPU is preempted, it will do VMENTER * no point in sending an IPI to SERIALIZE. */ return !vcpu_is_preempted(cpu); } void text_poke_sync(void) { smp_call_function_many_cond(cpu_possible_mask, do_sync_core, NULL, 1, text_poke_cond); sync_core(); } The 'same' for NOHZ_FULL, except we need to cmpxchg a value such that if the cmpxchg() succeeds we know the CPU is in userspace and will SERIALIZE on the next entry. Much like kvm_flush_tlb_others(). Anyway, that's all hand-wavey.. I'll let someone that cares about those things write actual patches :-)