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=-0.8 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 496C0C2D0DB for ; Wed, 29 Jan 2020 18:10:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2BCF520708 for ; Wed, 29 Jan 2020 18:10:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727367AbgA2SKd (ORCPT ); Wed, 29 Jan 2020 13:10:33 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50780 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726222AbgA2SKd (ORCPT ); Wed, 29 Jan 2020 13:10:33 -0500 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 00TI7T6x129481; Wed, 29 Jan 2020 13:10:17 -0500 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2xtpmtaccq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Jan 2020 13:10:17 -0500 Received: from m0098410.ppops.net (m0098410.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 00TI7k5O131193; Wed, 29 Jan 2020 13:10:16 -0500 Received: from ppma05wdc.us.ibm.com (1b.90.2fa9.ip4.static.sl-reverse.com [169.47.144.27]) by mx0a-001b2d01.pphosted.com with ESMTP id 2xtpmtacc5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Jan 2020 13:10:16 -0500 Received: from pps.filterd (ppma05wdc.us.ibm.com [127.0.0.1]) by ppma05wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id 00TI53W7010000; Wed, 29 Jan 2020 18:10:15 GMT Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by ppma05wdc.us.ibm.com with ESMTP id 2xrda741py-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Jan 2020 18:10:15 +0000 Received: from b03ledav006.gho.boulder.ibm.com (b03ledav006.gho.boulder.ibm.com [9.17.130.237]) by b03cxnp08027.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 00TIAEa456164636 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 29 Jan 2020 18:10:14 GMT Received: from b03ledav006.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8D75DC605D; Wed, 29 Jan 2020 18:10:14 +0000 (GMT) Received: from b03ledav006.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7928DC6062; Wed, 29 Jan 2020 18:10:14 +0000 (GMT) Received: from localhost (unknown [9.41.179.32]) by b03ledav006.gho.boulder.ibm.com (Postfix) with ESMTP; Wed, 29 Jan 2020 18:10:14 +0000 (GMT) Date: Wed, 29 Jan 2020 12:10:13 -0600 From: Scott Cheloha To: Nathan Lynch Cc: Nathan Fontenont , Rick Lindsley , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Michael Ellerman Subject: Re: [PATCH] powerpc/drmem: cache LMBs in xarray to accelerate lookup Message-ID: <20200129181013.lz6q5lpntnhwclqi@rascal.austin.ibm.com> References: <20200128221113.17158-1-cheloha@linux.ibm.com> <87pnf3i188.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87pnf3i188.fsf@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-01-29_05:2020-01-28,2020-01-29 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 phishscore=0 adultscore=0 clxscore=1015 priorityscore=1501 bulkscore=0 spamscore=0 suspectscore=1 impostorscore=0 malwarescore=0 mlxlogscore=999 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1911200001 definitions=main-2001290146 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 28, 2020 at 05:56:55PM -0600, Nathan Lynch wrote: > Scott Cheloha writes: > > LMB lookup is currently an O(n) linear search. This scales poorly when > > there are many LMBs. > > > > If we cache each LMB by both its base address and its DRC index > > in an xarray we can cut lookups to O(log n), greatly accelerating > > drmem initialization and memory hotplug. > > > > This patch introduces two xarrays of of LMBs and fills them during > > drmem initialization. The patch also adds two interfaces for LMB > > lookup. > > Good but can you replace the array of LMBs altogether > (drmem_info->lmbs)? xarray allows iteration over the members if needed. I don't think we can without potentially changing the current behavior. The current behavior in dlpar_memory_{add,remove}_by_ic() is to advance linearly through the array from the LMB with the matching DRC index. Iteration through the xarray via xa_for_each_start() will return LMBs indexed with monotonically increasing DRC indices. Are they equivalent? Or can we have an LMB with a smaller DRC index appear at a greater offset in the array? If the following condition is possible: drmem_info->lmbs[i].drc_index > drmem_info->lmbs[j].drc_index where i < j, then we have a possible behavior change because xa_for_each_start() may not return a contiguous array slice. It might "leap backwards" in the array. Or it might skip over a chunk of LMBs.