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_HELO_NONE,SPF_PASS 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 78A21C5AE59 for ; Tue, 10 Sep 2019 22:11:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4EBBE216F4 for ; Tue, 10 Sep 2019 22:11:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725965AbfIJWLx (ORCPT ); Tue, 10 Sep 2019 18:11:53 -0400 Received: from mga05.intel.com ([192.55.52.43]:38804 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725880AbfIJWLw (ORCPT ); Tue, 10 Sep 2019 18:11:52 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Sep 2019 15:11:51 -0700 X-IronPort-AV: E=Sophos;i="5.64,490,1559545200"; d="scan'208";a="268551180" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Sep 2019 15:11:50 -0700 Message-ID: <3de2409415b20440d5c8f3016ed78fde3d106dc8.camel@linux.intel.com> Subject: Re: [PATCH v9 1/8] mm: Add per-cpu logic to page shuffling From: Alexander Duyck To: David Hildenbrand , Alexander Duyck , virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org, mst@redhat.com, catalin.marinas@arm.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, will@kernel.org, linux-arm-kernel@lists.infradead.org, osalvador@suse.de Cc: yang.zhang.wz@gmail.com, pagupta@redhat.com, konrad.wilk@oracle.com, nitesh@redhat.com, riel@surriel.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, ying.huang@intel.com, pbonzini@redhat.com, dan.j.williams@intel.com, fengguang.wu@intel.com, kirill.shutemov@linux.intel.com Date: Tue, 10 Sep 2019 15:11:50 -0700 In-Reply-To: <0df2e5d0-af92-04b4-aa7d-891387874039@redhat.com> References: <20190907172225.10910.34302.stgit@localhost.localdomain> <20190907172512.10910.74435.stgit@localhost.localdomain> <0df2e5d0-af92-04b4-aa7d-891387874039@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, 2019-09-09 at 10:14 +0200, David Hildenbrand wrote: > On 07.09.19 19:25, Alexander Duyck wrote: > > From: Alexander Duyck > > > > Change the logic used to generate randomness in the suffle path so that we > > can avoid cache line bouncing. The previous logic was sharing the offset > > and entropy word between all CPUs. As such this can result in cache line > > bouncing and will ultimately hurt performance when enabled. > > So, usually we perform such changes if there is real evidence. Do you > have any such performance numbers to back your claims? I don't have any numbers. From what I can tell the impact is small enough that this doesn't really have much impact. With that being the case I can probably just drop this patch. I will instead just use "rand & 1" in the 2nd patch to generate the return value which was what was previously done in add_to_free_area_random.