From patchwork Mon Jul 10 19:48:53 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13307545 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 D26D3C001B0 for ; Mon, 10 Jul 2023 19:50:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231355AbjGJTuA (ORCPT ); Mon, 10 Jul 2023 15:50:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51458 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230196AbjGJTt7 (ORCPT ); Mon, 10 Jul 2023 15:49:59 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA8DC195 for ; Mon, 10 Jul 2023 12:49:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689018553; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=tuOgUub1usvf3/oKhasyYKOBssVvHMJ2wullIZXHhCs=; b=AZlu1AinDdl8JH5zVbcyECICej4wbilIxfNAecrJ0rM7avQ/YvTKFGHoXaicaw0YO2XoLt giZShUiHgdT8z5tiUYOg+ka/tHi1OhcTg1Pn3GMJipQtKehen0R0/oR+TnY9Dub33vo3L6 vpkk4jBC9Rq5M4ymh44OQe58ZgxEr60= 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-374-wRDRh4PaNGS3XCv-c4EfsA-1; Mon, 10 Jul 2023 15:49:08 -0400 X-MC-Unique: wRDRh4PaNGS3XCv-c4EfsA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3D3C81006849; Mon, 10 Jul 2023 19:49:07 +0000 (UTC) Received: from llong.com (unknown [10.22.18.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id BDF55111E3E6; Mon, 10 Jul 2023 19:49:05 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , Jonathan Corbet , "Rafael J . Wysocki" Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Randy Dunlap , Waiman Long Subject: [PATCH v5 0/4] x86/speculation: Disable IBRS when idle Date: Mon, 10 Jul 2023 15:48:53 -0400 Message-Id: <20230710194857.2898284-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org v5: - Update comment in patch 1. - Minor doc update and code twist in patch 4 as suggested by Peter and Randy. v4: - Add a new __update_spec_ctrl() helper in patch 1. - Rebased to the latest linux kernel. v3: - Drop patches 1 ("x86/speculation: Provide a debugfs file to dump SPEC_CTRL MSRs") and 5 ("x86/idle: Disable IBRS entering mwait idle and enable it on wakeup") for now. - Drop the MSR restoration code in ("x86/idle: Disable IBRS when cpu is offline") as native_play_dead() does not return. - For patch ("intel_idle: Add ibrs_off module parameter to force disable IBRS"), change the name from "no_ibrs" to "ibrs_off" and document the new parameter in intel_idle.rst. For Intel processors that need to turn on IBRS to protect against Spectre v2 and Retbleed, the IBRS bit in the SPEC_CTRL MSR affects the performance of the whole core even if only one thread is turning it on when running in the kernel. For user space heavy applications, the performance impact of occasionally turning IBRS on during syscalls shouldn't be significant. Unfortunately, that is not the case when the sibling thread is idling in the kernel. In that case, the performance impact can be significant. When DPDK is running on an isolated CPU thread processing network packets in user space while its sibling thread is idle. The performance of the busy DPDK thread with IBRS on and off in the sibling idle thread are: IBRS on IBRS off ------- -------- packets/second: 7.8M 10.4M avg tsc cycles/packet: 282.26 209.86 This is a 25% performance degradation. The test system is a Intel Xeon 4114 CPU @ 2.20GHz. Commit bf5835bcdb96 ("intel_idle: Disable IBRS during long idle") disables IBRS when the CPU enters long idle (C6 or below). However, there are existing users out there who have set "intel_idle.max_cstate=1" to decrease latency. Those users won't be able to benefit from this commit. This patch series extends this commit by providing a new "intel_idle.ibrs_off" module parameter to force disable IBRS even when "intel_idle.max_cstate=1" at the expense of increased IRQ response latency. It also includes a commit to allow the disabling of IBRS when a CPU becomes offline. Waiman Long (4): x86/speculation: Add __update_spec_ctrl() helper x86/idle: Disable IBRS when cpu is offline intel_idle: Use __update_spec_ctrl() in intel_idle_ibrs() intel_idle: Add ibrs_off module parameter to force disable IBRS Documentation/admin-guide/pm/intel_idle.rst | 17 ++++++++++++++++- arch/x86/include/asm/nospec-branch.h | 12 +++++++++++- arch/x86/kernel/smpboot.c | 8 ++++++++ drivers/idle/intel_idle.c | 15 ++++++++++++--- 4 files changed, 47 insertions(+), 5 deletions(-)