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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 ABEA5C43441 for ; Thu, 22 Nov 2018 00:01:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B78E20663 for ; Thu, 22 Nov 2018 00:01:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B78E20663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388426AbeKVKhs (ORCPT ); Thu, 22 Nov 2018 05:37:48 -0500 Received: from mga06.intel.com ([134.134.136.31]:43980 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726862AbeKVKhr (ORCPT ); Thu, 22 Nov 2018 05:37:47 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Nov 2018 16:01:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,263,1539673200"; d="scan'208";a="251635036" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.7.201.126]) by orsmga004.jf.intel.com with ESMTP; 21 Nov 2018 16:01:08 -0800 Received: by tassilo.localdomain (Postfix, from userid 1000) id 5EA90301846; Wed, 21 Nov 2018 16:01:08 -0800 (PST) Date: Wed, 21 Nov 2018 16:01:08 -0800 From: Andi Kleen To: Thomas Gleixner Cc: LKML , x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Linus Torvalds , Jiri Kosina , Tom Lendacky , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Dave Stewart , Kees Cook Subject: Re: [patch 17/24] x86/speculation: Move IBPB control out of switch_mm() Message-ID: <20181122000108.GJ13936@tassilo.jf.intel.com> References: <20181121201430.559770965@linutronix.de> <20181121201723.948990148@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181121201723.948990148@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > + * This could be optimized by keeping track of the last > + * user task per cpu and avoiding the barrier when the task > + * is immediately scheduled back and the thread inbetween > + * was a kernel thread. It's dubious whether that'd be > + * worth the extra load/store and conditional operations. > + * Keep it optimized for the common case where the TIF bit > + * is not set. > + */ The optimization was there before and you removed it? It's quite important for switching to idle and back. With your variant short IOs that do short idle waits will be badly impacted. -Andi