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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,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 00A81C433EA for ; Tue, 28 Jul 2020 10:39:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D3C322083E for ; Tue, 28 Jul 2020 10:39:24 +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="Zxsoqojn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728699AbgG1KjV (ORCPT ); Tue, 28 Jul 2020 06:39:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56556 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728566AbgG1KjV (ORCPT ); Tue, 28 Jul 2020 06:39:21 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BEF3EC061794; Tue, 28 Jul 2020 03:39:20 -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=ypNJAwGRLRbYYnJEfcTCKIzmFirwGZ/k/RvbvuVZ8q4=; b=ZxsoqojnivhdOtNFQ7ijw8tFIS DW2+ZZdVqI+YTlXRfXfozGEbH0saMYPSlKwQFgNptwke3nKub9qOKLzuTljpCmSmuIi4DoV5ZmT+a ORDvwrsMfcuqK3Ko+zIHqF3P99gL9wRxJQHCLF8Fgx7lh7EslkDSBjnJ55dmRuZNkWhL0idV+rLVt MLT4DVYgUuZ2T/1BHmgk0so5e2riO7lt2CnymYnKd1s0zn87qz7kg+AcOzOe38dctjCghsWQdxtcB co4YxEvoJTQ21Q67Z6VyRIfwG33K2mPvRHnXc9YJRwSelSn+vgiQvyxBxhi5mdEa8Msv9zrnyTlHD rCwmh9nw==; 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 1k0N0n-0006gK-NF; Tue, 28 Jul 2020 10:39:09 +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 561D2304BAE; Tue, 28 Jul 2020 12:39:07 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 20888238A58A4; Tue, 28 Jul 2020 12:39:07 +0200 (CEST) Date: Tue, 28 Jul 2020 12:39:07 +0200 From: peterz@infradead.org To: Xi Wang Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Mel Gorman , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, suravee.suthikulpanit@amd.com, thomas.lendacky@amd.com Subject: Re: [PATCH] sched: Make select_idle_sibling search domain configurable Message-ID: <20200728103907.GT119549@hirez.programming.kicks-ass.net> References: <20200728070131.1629670-1-xii@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200728070131.1629670-1-xii@google.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jul 28, 2020 at 12:01:31AM -0700, Xi Wang wrote: > The scope of select_idle_sibling idle cpu search is LLC. This > becomes a problem for the AMD CCX architecture, as the sd_llc is only > 4 cores. On a many core machine, the range of search is too small to > reach a satisfactory level of statistical multiplexing / efficient > utilization of short idle time slices. > > With this patch idle sibling search is detached from LLC and it > becomes run time configurable. To reduce search and migration > overheads, a presearch domain is added. The presearch domain will be > searched first before the "main search" domain, e.g.: > > sysctl_sched_wake_idle_domain == 2 ("MC" domain) > sysctl_sched_wake_idle_presearch_domain == 1 ("DIE" domain) > > Presearch will go through 4 cores of a CCX. If no idle cpu is found > during presearch, full search will go through the remaining cores of > a cpu socket. *groan*, this is horrific :-( It is also in direct conflict with people wanting to make it smaller. On top of that, a domain number is a terrible terrible interface. They aren't even available without SCHED_DEBUG on. What is the inter-L3 latency? Going by this that had better be awesome. And if this Infinity Fabric stuff if highly effective in effectively merging L3s -- analogous to what Intel does with it's cache slices, then should we not change the AMD topology setup instead of this 'thing'? Also, this commit: 051f3ca02e46 ("sched/topology: Introduce NUMA identity node sched domain") seems to suggest L3 is actually bigger. Suravee, can you please comment?