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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 B1C52C43387 for ; Thu, 3 Jan 2019 22:18:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E018217F5 for ; Thu, 3 Jan 2019 22:18:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728419AbfACWSQ (ORCPT ); Thu, 3 Jan 2019 17:18:16 -0500 Received: from mga02.intel.com ([134.134.136.20]:53433 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728379AbfACWSQ (ORCPT ); Thu, 3 Jan 2019 17:18:16 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Jan 2019 14:18:15 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,436,1539673200"; d="scan'208";a="123910284" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.7.201.137]) by orsmga001.jf.intel.com with ESMTP; 03 Jan 2019 14:18:15 -0800 Received: by tassilo.localdomain (Postfix, from userid 1000) id 55078301B2E; Thu, 3 Jan 2019 14:18:15 -0800 (PST) From: Andi Kleen To: Nadav Amit Cc: Ingo Molnar , Andy Lutomirski , Peter Zijlstra , Josh Poimboeuf , Edward Cree , "H . Peter Anvin" , Thomas Gleixner , LKML , Nadav Amit , X86 ML , Paolo Abeni , Borislav Petkov , David Woodhouse , adrian.hunter@intel.com Subject: Re: [RFC v2 0/6] x86: dynamic indirect branch promotion References: <20181231072112.21051-1-namit@vmware.com> Date: Thu, 03 Jan 2019 14:18:15 -0800 In-Reply-To: <20181231072112.21051-1-namit@vmware.com> (Nadav Amit's message of "Sun, 30 Dec 2018 23:21:06 -0800") Message-ID: <87zhshe66w.fsf@linux.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Nadav Amit writes: > > - Do we use periodic learning or not? Josh suggested to reconfigure the > branches whenever a new target is found. However, I do not know at > this time how to do learning efficiently, without making learning much > more expensive. FWIW frequent patching will likely completely break perf Processor Trace decoding, which needs a somewhat stable kernel text image to decode the traces generated by the CPU. Right now it relies on kcore dumped after the trace usually being stable because jumplabel changes happen only infrequently. But if you start patching frequently this assumption will break. You would either need a way to turn this off, or provide updates for every change to the trace, so that the decoder can keep track. -Andi