From patchwork Thu Jun 22 00:36:00 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13288100 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 A3C49EB64D7 for ; Thu, 22 Jun 2023 00:38:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229830AbjFVAiK (ORCPT ); Wed, 21 Jun 2023 20:38:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229889AbjFVAiJ (ORCPT ); Wed, 21 Jun 2023 20:38:09 -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 99A151997 for ; Wed, 21 Jun 2023 17:36:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687394208; 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=JClsVInx+SfJQwVlXcLVSsPnUQ6NqCBnYMZfU8zrapQ=; b=H5217mcVJ6cf2JO2feUfRdB67a+Y8vg1UkV3L/lTikVCK0tK6dhWZUpHaiDF7G4nGF8xiy tX+bXKBP0aRau5/boQn0hRvsQy45ttkcXFGUT3Ka+qCf01QtaK2zi81VMvYmn/ET/fi4Cc EgB6ETMa8JPGYpO+ITmIUIgMYe/Aagc= 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-468-h3nYqPbcM1-QS6yb3y4lTg-1; Wed, 21 Jun 2023 20:36:43 -0400 X-MC-Unique: h3nYqPbcM1-QS6yb3y4lTg-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 ECB4E8C5868; Thu, 22 Jun 2023 00:36:41 +0000 (UTC) Received: from llong.com (unknown [10.22.33.143]) by smtp.corp.redhat.com (Postfix) with ESMTP id 033EE112132C; Thu, 22 Jun 2023 00:36:23 +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 Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Waiman Long Subject: [PATCH v3 0/3] x86/speculation: Disable IBRS when idle Date: Wed, 21 Jun 2023 20:36:00 -0400 Message-Id: <20230622003603.1188364-1-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 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 (3): x86/idle: Disable IBRS when cpu is offline intel_idle: Sync up the SPEC_CTRL MSR value to x86_spec_ctrl_current intel_idle: Add ibrs_off module parameter to force disable IBRS Documentation/admin-guide/pm/intel_idle.rst | 17 +++++++++++++++- arch/x86/kernel/smpboot.c | 10 ++++++++++ drivers/idle/intel_idle.c | 22 +++++++++++++++++---- 3 files changed, 44 insertions(+), 5 deletions(-)