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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 8CBB3C433E6 for ; Tue, 16 Feb 2021 16:33:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5BA4364E13 for ; Tue, 16 Feb 2021 16:33:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230291AbhBPQdt (ORCPT ); Tue, 16 Feb 2021 11:33:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230149AbhBPQdr (ORCPT ); Tue, 16 Feb 2021 11:33:47 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 52860C061756 for ; Tue, 16 Feb 2021 08:33:07 -0800 (PST) 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=wQUTkY1oq1agJ9hryvP+SMygbLHZkeBCm/G5cT/kGuo=; b=L9UNtrPvySnvc93doqa6NJBqkt 1Z/lUKkPgg5l3xrMVnFrH8OvSv6WmaAB5vjFrL+1qLrCSTbhvWwa5HkIpwoJdrULyM08G7xCUHvvX cVcNOAwEVZI+/iKz4IyeTFz+Krz2GgWvdGkJENhQnw4zaI77+BIYJUjAC19zozAYs5/OvzjfpWywR 75BECY3zrlvxcAabJU2Zgr2bgAu4jWmPpTQDV9FWpLx73KCCnOsNVaTM24jn77vFo/bHX88AXRxIw 0i2DoIXQ1T2CH0tbgEr8kSpnIb6+Z2tbBGOXrpq7cm+xgYco4VXzxTaTx/LiPrxg44zAo2Yln+oYe SpCP9PGQ==; 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 1lC3HW-0003Ew-3U; Tue, 16 Feb 2021 16:32:58 +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 DA06A3035D4; Tue, 16 Feb 2021 17:32:52 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id C5EFC2BC42A1E; Tue, 16 Feb 2021 17:32:52 +0100 (CET) Date: Tue, 16 Feb 2021 17:32:52 +0100 From: Peter Zijlstra To: Nadav Amit Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Andy Lutomirski , Dave Hansen , Nadav Amit , Rik van Riel , Josh Poimboeuf Subject: Re: [PATCH v5 1/8] smp: Run functions concurrently in smp_call_function_many_cond() Message-ID: References: <20210209221653.614098-1-namit@vmware.com> <20210209221653.614098-2-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210209221653.614098-2-namit@vmware.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 09, 2021 at 02:16:46PM -0800, Nadav Amit wrote: > From: Nadav Amit > > Currently, on_each_cpu() and similar functions do not exploit the > potential of concurrency: the function is first executed remotely and > only then it is executed locally. Functions such as TLB flush can take > considerable time, so this provides an opportunity for performance > optimization. > > To do so, modify smp_call_function_many_cond(), to allows the callers to > provide a function that should be executed (remotely/locally), and run > them concurrently. Keep other smp_call_function_many() semantic as it is > today for backward compatibility: the called function is not executed in > this case locally. > > smp_call_function_many_cond() does not use the optimized version for a > single remote target that smp_call_function_single() implements. For > synchronous function call, smp_call_function_single() keeps a > call_single_data (which is used for synchronization) on the stack. > Interestingly, it seems that not using this optimization provides > greater performance improvements (greater speedup with a single remote > target than with multiple ones). Presumably, holding data structures > that are intended for synchronization on the stack can introduce > overheads due to TLB misses and false-sharing when the stack is used for > other purposes. > > Reviewed-by: Dave Hansen > Cc: Peter Zijlstra > Cc: Rik van Riel > Cc: Thomas Gleixner > Cc: Andy Lutomirski > Cc: Josh Poimboeuf > Signed-off-by: Nadav Amit Kernel-CI is giving me a regression that's most likely this patch: https://kernelci.org/test/case/id/602bdd621c979f83faaddcc6/ I'm not sure I can explain it yet. It did get me looking at on_each_cpu() and it appears that wants to be converted too, something like the below perhaps. --- a/kernel/smp.c +++ b/kernel/smp.c @@ -848,14 +848,7 @@ void __init smp_init(void) */ void on_each_cpu(smp_call_func_t func, void *info, int wait) { - unsigned long flags; - - preempt_disable(); - smp_call_function(func, info, wait); - local_irq_save(flags); - func(info); - local_irq_restore(flags); - preempt_enable(); + on_each_cpu_mask(cpu_online_mask, func, info, wait); } EXPORT_SYMBOL(on_each_cpu); @@ -878,15 +871,7 @@ EXPORT_SYMBOL(on_each_cpu); void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, void *info, bool wait) { - unsigned int scf_flags; - - scf_flags = SCF_RUN_LOCAL; - if (wait) - scf_flags |= SCF_WAIT; - - preempt_disable(); - smp_call_function_many_cond(mask, func, info, scf_flags, NULL); - preempt_enable(); + on_each_cpu_cond_mask(NULL, func, info, wait, mask); } EXPORT_SYMBOL(on_each_cpu_mask); @@ -912,6 +897,13 @@ EXPORT_SYMBOL(on_each_cpu_mask); * You must not call this function with disabled interrupts or * from a hardware interrupt handler or from a bottom half handler. */ +void on_each_cpu_cond(smp_cond_func_t cond_func, smp_call_func_t func, + void *info, bool wait) +{ + on_each_cpu_cond_mask(cond_func, func, info, wait, cpu_online_mask); +} +EXPORT_SYMBOL(on_each_cpu_cond); + void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func, void *info, bool wait, const struct cpumask *mask) { @@ -926,13 +918,6 @@ void on_each_cpu_cond_mask(smp_cond_func } EXPORT_SYMBOL(on_each_cpu_cond_mask); -void on_each_cpu_cond(smp_cond_func_t cond_func, smp_call_func_t func, - void *info, bool wait) -{ - on_each_cpu_cond_mask(cond_func, func, info, wait, cpu_online_mask); -} -EXPORT_SYMBOL(on_each_cpu_cond); - static void do_nothing(void *unused) { } ~