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 27AE1CDB482 for ; Thu, 19 Oct 2023 04:38:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232552AbjJSEir (ORCPT ); Thu, 19 Oct 2023 00:38:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229894AbjJSEio (ORCPT ); Thu, 19 Oct 2023 00:38:44 -0400 Received: from gandalf.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A4FA811F for ; Wed, 18 Oct 2023 21:38:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ellerman.id.au; s=201909; t=1697690320; bh=Rv0RE/UnlB8ImLuckgrocUTCXXYAwShhb75jdX29cjc=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=JC0wjKhxL2KrO9rfTQylV0wrN1YQQTse08jfgDBNxbyiJkS4q1SvRMJIWc9XG81gy LcHjOsq5IYrWqiuG48TdYsX0dhkH1VpWMq1uHO5zxGpWlmKIE+tMdgcKSZpW1s1Y27 9Gaas4gEdVokMsT90w7cSvRiQB4Wa1Yl12Myy6rlAycLx5YPkbTjG7xtcwMZx2inmA BlnmzP8TYW7X+Kg6wbXhogcS33ZvEpxWSp29K7T6Swpv2E+Eiq8buPG+rNlg/ta9Xg mOTTQKQIjXqG3MtyRMTa3b1hPWklNMPmud9M2pWbfd6LpRf9lvgCsZwZkAcWdjziyZ AgTu/xGIiB7ug== Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4S9w2m3N7Wz4xZS; Thu, 19 Oct 2023 15:38:40 +1100 (AEDT) From: Michael Ellerman To: Srikar Dronamraju Cc: linuxppc-dev , Srikar Dronamraju , Christophe Leroy , Nicholas Piggin , Peter Zijlstra , Rohan McLure , Valentin Schneider , Josh Poimboeuf , Mark Rutland , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/6] powerpc/smp: Enable Asym packing for cores on shared processor In-Reply-To: <20231018163751.2423181-3-srikar@linux.vnet.ibm.com> References: <20231018163751.2423181-1-srikar@linux.vnet.ibm.com> <20231018163751.2423181-3-srikar@linux.vnet.ibm.com> Date: Thu, 19 Oct 2023 15:38:40 +1100 Message-ID: <87v8b35ir3.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Srikar Dronamraju writes: > If there are shared processor LPARs, underlying Hypervisor can have more > virtual cores to handle than actual physical cores. > > Starting with Power 9, a core has 2 nearly independent thread groups. You need to be clearer here that you're talking about "big cores", not SMT4 cores as seen on bare metal systems. > On a shared processors LPARs, it helps to pack threads to lesser number > of cores so that the overall system performance and utilization > improves. PowerVM schedules at a core level. Hence packing to fewer > cores helps. > > For example: Lets says there are two 8-core Shared LPARs that are > actually sharing a 8 Core shared physical pool, each running 8 threads > each. Then Consolidating 8 threads to 4 cores on each LPAR would help > them to perform better. This is because each of the LPAR will get > 100% time to run applications and there will no switching required by > the Hypervisor. > > To achieve this, enable SD_ASYM_PACKING flag at CACHE, MC and DIE level. .. when the system is running in shared processor mode and has big cores. cheers > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > index 37c41297c9ce..498c2d51fc20 100644 > --- a/arch/powerpc/kernel/smp.c > +++ b/arch/powerpc/kernel/smp.c > @@ -1009,9 +1009,20 @@ static int powerpc_smt_flags(void) > */ > static int powerpc_shared_cache_flags(void) > { > + if (static_branch_unlikely(&powerpc_asym_packing)) > + return SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING; > + > return SD_SHARE_PKG_RESOURCES; > } > > +static int powerpc_shared_proc_flags(void) > +{ > + if (static_branch_unlikely(&powerpc_asym_packing)) > + return SD_ASYM_PACKING; > + > + return 0; > +} > + > /* > * We can't just pass cpu_l2_cache_mask() directly because > * returns a non-const pointer and the compiler barfs on that. > @@ -1048,8 +1059,8 @@ static struct sched_domain_topology_level powerpc_topology[] = { > { cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) }, > #endif > { shared_cache_mask, powerpc_shared_cache_flags, SD_INIT_NAME(CACHE) }, > - { cpu_mc_mask, SD_INIT_NAME(MC) }, > - { cpu_cpu_mask, SD_INIT_NAME(DIE) }, > + { cpu_mc_mask, powerpc_shared_proc_flags, SD_INIT_NAME(MC) }, > + { cpu_cpu_mask, powerpc_shared_proc_flags, SD_INIT_NAME(DIE) }, > { NULL, }, > }; > > @@ -1687,6 +1698,8 @@ static void __init fixup_topology(void) > if (cpu_has_feature(CPU_FTR_ASYM_SMT)) { > pr_info_once("Enabling Asymmetric SMT scheduling\n"); > static_branch_enable(&powerpc_asym_packing); > + } else if (is_shared_processor() && has_big_cores) { > + static_branch_enable(&powerpc_asym_packing); > } > > #ifdef CONFIG_SCHED_SMT > -- > 2.31.1