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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 926BDC11F68 for ; Fri, 2 Jul 2021 12:57:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74122611F1 for ; Fri, 2 Jul 2021 12:57:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232305AbhGBNAG (ORCPT ); Fri, 2 Jul 2021 09:00:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230241AbhGBNAF (ORCPT ); Fri, 2 Jul 2021 09:00:05 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A66B5C061762 for ; Fri, 2 Jul 2021 05:57:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GW7O2b9giTKhc36P5PVe5SwIe/E7zGRfMUdGgkuBFMY=; b=WJOsav2YAO5yyYWf5MznMqYZdP Gw9HxQkqAhef9jFMBEACaXuinWd2eSCWKgz+UFAXi4hgLiHI9CVOKOsGvEmLK+NqQHxyczcQevzz4 rRDem+Xh8p41XL6sWk6WCdqzt0kgFlxl08Wr8OdzY/ZQN1hJDFf6nh3JJvpO0IBFY34OaMLsthLKJ 1EXiZbiOoQSR4/5ZbbMjo4hW5mzD3Ss3cJxE/Khy70GoXFKpox4H2j+/cZRhKbgHopYgMxyiyazfa +EYJg9yTJW0pxsFft0Dx6kseOxldzX9ioS/l2fZkJKnXnPsMuI/TuqiuiI1D3L0+zXmNEFyi9VoPy GXULI5gg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1lzIj3-007i7k-5J; Fri, 02 Jul 2021 12:57:03 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 707673002D3; Fri, 2 Jul 2021 14:56:56 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 38C772B981DA0; Fri, 2 Jul 2021 14:56:56 +0200 (CEST) Date: Fri, 2 Jul 2021 14:56:56 +0200 From: Peter Zijlstra To: Bill Wendling Cc: Linus Torvalds , Kees Cook , Linux Kernel Mailing List , Bill Wendling , Catalin Marinas , clang-built-linux , Fangrui Song , Heiko Carstens , Jarmo Tiitto , Lukas Bulwahn , Mark Rutland , Masahiro Yamada , Miguel Ojeda , Nathan Chancellor , Nick Desaulniers , Peter Oberparleiter , Sami Tolvanen , Will Deacon Subject: Re: [GIT PULL] Clang feature updates for v5.14-rc1 Message-ID: References: <202106281231.E99B92BB13@keescook> <202106291311.20AB10D04@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 02, 2021 at 05:46:46AM -0700, Bill Wendling wrote: > On Tue, Jun 29, 2021 at 2:04 PM Linus Torvalds > wrote: > > > > On Tue, Jun 29, 2021 at 1:44 PM Kees Cook wrote: > > > > > > > > And it causes the kernel to be bigger and run slower. > > > > > > Right -- that's expected. It's not designed to be the final kernel > > > someone uses. :) > > > > Well, from what I've seen, you actually want to run real loads in > > production environments for PGO to actually be anything but a bogus > > "performance benchmarks only" kind of thing. > > > The reason we use PGO in this way is because we _cannot_ release a > kernel into production that hasn't had PGO applied to it. The > performance of a non-PGO'ed kernel is a non-starter for rollout. We > try our best to replicate this environment for the benchmarks, which > is the only sane way to do this. I can't imagine that we're the only > ones who run up against this chicken-and-egg problem. > > For why we don't use sampling, PGO gives a better performance boost > from an instrumented kernel rather than a sampled profile. I'll work > on getting statistics to show this. I've asked this before; *what* is missing from LBR samples that's reponsible for the performance gap?