From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752345AbaJYUjl (ORCPT ); Sat, 25 Oct 2014 16:39:41 -0400 Received: from numascale.com ([213.162.240.84]:50560 "EHLO numascale.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751921AbaJYUjj (ORCPT ); Sat, 25 Oct 2014 16:39:39 -0400 Message-ID: <544B4A4C.5070807@numascale.com> Date: Sat, 25 Oct 2014 14:59:24 +0800 From: Daniel J Blueman Organization: Numascale AS User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: "Paul E. McKenney" CC: Steffen Persvold , LKML Subject: RCU fanout leaf balancing Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cpanel21.proisp.no X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - numascale.com X-Get-Message-Sender-Via: cpanel21.proisp.no: authenticated_id: daniel@numascale.com X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, Finding earlier reference to increasing RCU fanout leaf for the purpose of "decrease[ing] cache-miss overhead for large systems", would your suggestion be to increase the value to the next hierarchy core-count above 16? If we have say 32 interconnected 48-core servers; 3 sockets of dual-node 8-core Opteron 6300s, so 1536 cores in all. Latency across the coherent interconnect is O(100x) higher than the internal Hypertransport interconnect, so if we set RCU_FANOUT_LEAF to 48 to keep leaf-checking local to one Hypertransport fabric, what wisdom would one use for RCU_FANOUT? 4x leaf? Or, would it be more cache-friendly to set RCU_FANOUT_LEAF to 8 and RCU_FANOUT to 48? Many thanks, Daniel -- Daniel J Blueman Principal Software Engineer, Numascale