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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 135FEC43613 for ; Fri, 21 Jun 2019 08:15:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB7DE208CA for ; Fri, 21 Jun 2019 08:15:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726074AbfFUIPg (ORCPT ); Fri, 21 Jun 2019 04:15:36 -0400 Received: from verein.lst.de ([213.95.11.211]:36549 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726030AbfFUIPg (ORCPT ); Fri, 21 Jun 2019 04:15:36 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id BAE6368C4E; Fri, 21 Jun 2019 10:15:01 +0200 (CEST) Date: Fri, 21 Jun 2019 10:15:01 +0200 From: Christoph Hellwig To: Linus Torvalds Cc: Nicholas Piggin , Andrey Konovalov , Benjamin Herrenschmidt , Rich Felker , "David S. Miller" , Christoph Hellwig , James Hogan , Khalid Aziz , Linux List Kernel Mailing , linux-mips@vger.kernel.org, Linux-MM , linuxppc-dev@lists.ozlabs.org, Linux-sh list , Michael Ellerman , Paul Burton , Paul Mackerras , sparclinux@vger.kernel.org, the arch/x86 maintainers , Yoshinori Sato Subject: Re: [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in a structure Message-ID: <20190621081501.GA17718@lst.de> References: <20190611144102.8848-1-hch@lst.de> <20190611144102.8848-17-hch@lst.de> <1560300464.nijubslu3h.astroid@bobo.none> <1561032202.0qfct43s2c.astroid@bobo.none> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Thu, Jun 20, 2019 at 10:21:46AM -0700, Linus Torvalds wrote: > Hmm. Honestly, I've never seen anything like that in any kernel profiles. > > Compared to the problems I _do_ see (which is usually the obvious > cache misses, and locking), it must either be in the noise or it's > some problem specific to whatever CPU you are doing performance work > on? > > I've occasionally seen pipeline hiccups in profiles, but it's usually > been either some serious glass jaw of the core, or it's been something > really stupid we did (or occasionally that the compiler did: one in > particular I remember was how there was a time when gcc would narrow > stores when it could, so if you set a bit in a word, it would do it > with a byte store, and then when you read the whole word afterwards > you'd get a major pipeline stall and it happened to show up in some > really hot paths). I've not seen any difference in the GUP bench output here ar all. But I'm fine with skipping this patch for now, I have a potential series I'm looking into that would benefit a lot from it, but we can discusss it in that context and make sure all the other works gets in in time.