From patchwork Wed May 20 18:26:45 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Jordan X-Patchwork-Id: 1294583 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 49S1kg3d26z9sTC for ; Thu, 21 May 2020 04:39:39 +1000 (AEST) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=oracle.com header.i=@oracle.com header.a=rsa-sha256 header.s=corp-2020-01-29 header.b=P3/+t99s; dkim-atps=neutral Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49S1kg2pqLzDqhl for ; 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Wed, 20 May 2020 18:27:11 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 315020rdjx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 20 May 2020 18:27:10 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 04KIR8V3008161; Wed, 20 May 2020 18:27:08 GMT Received: from localhost.localdomain (/98.229.125.203) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 20 May 2020 11:27:08 -0700 From: Daniel Jordan To: Andrew Morton , Herbert Xu , Steffen Klassert Subject: [PATCH v2 7/7] padata: document multithreaded jobs Date: Wed, 20 May 2020 14:26:45 -0400 Message-Id: <20200520182645.1658949-8-daniel.m.jordan@oracle.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200520182645.1658949-1-daniel.m.jordan@oracle.com> References: <20200520182645.1658949-1-daniel.m.jordan@oracle.com> MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9627 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 bulkscore=0 suspectscore=0 phishscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005200148 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9627 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 spamscore=0 mlxlogscore=999 clxscore=1015 priorityscore=1501 cotscore=-2147483648 impostorscore=0 bulkscore=0 adultscore=0 malwarescore=0 phishscore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005200148 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: David Hildenbrand , Peter Zijlstra , Dave Hansen , Michal Hocko , linux-mm@kvack.org, Steven Sistare , Pavel Machek , Alexander Duyck , linux-s390@vger.kernel.org, Jonathan Corbet , Daniel Jordan , Jason Gunthorpe , Zi Yan , Robert Elliott , Pavel Tatashin , Shile Zhang , Josh Triplett , Alex Williamson , Kirill Tkhai , Dan Williams , Randy Dunlap , linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, Tejun Heo , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Add Documentation for multithreaded jobs. Signed-off-by: Daniel Jordan --- Documentation/core-api/padata.rst | 41 +++++++++++++++++++++++-------- 1 file changed, 31 insertions(+), 10 deletions(-) diff --git a/Documentation/core-api/padata.rst b/Documentation/core-api/padata.rst index 9a24c111781d9..b7e047af993e8 100644 --- a/Documentation/core-api/padata.rst +++ b/Documentation/core-api/padata.rst @@ -4,23 +4,26 @@ The padata parallel execution mechanism ======================================= -:Date: December 2019 +:Date: April 2020 Padata is a mechanism by which the kernel can farm jobs out to be done in -parallel on multiple CPUs while retaining their ordering. It was developed for -use with the IPsec code, which needs to be able to perform encryption and -decryption on large numbers of packets without reordering those packets. The -crypto developers made a point of writing padata in a sufficiently general -fashion that it could be put to other uses as well. +parallel on multiple CPUs while optionally retaining their ordering. -Usage -===== +It was originally developed for IPsec, which needs to perform encryption and +decryption on large numbers of packets without reordering those packets. This +is currently the sole consumer of padata's serialized job support. + +Padata also supports multithreaded jobs, splitting up the job evenly while load +balancing and coordinating between threads. + +Running Serialized Jobs +======================= Initializing ------------ -The first step in using padata is to set up a padata_instance structure for -overall control of how jobs are to be run:: +The first step in using padata to run parallel jobs is to set up a +padata_instance structure for overall control of how jobs are to be run:: #include @@ -162,6 +165,24 @@ functions that correspond to the allocation in reverse:: It is the user's responsibility to ensure all outstanding jobs are complete before any of the above are called. +Running Multithreaded Jobs +========================== + +A multithreaded job has a main thread and zero or more helper threads, with the +main thread participating in the job and then waiting until all helpers have +finished. padata splits the job into units called chunks, where a chunk is a +piece of the job that one thread completes in one call to the thread function. + +A user has to do three things to run a multithreaded job. First, describe the +job by defining a padata_mt_job structure, which is explained in the Interface +section. This includes a pointer to the thread function, which padata will +call each time it assigns a job chunk to a thread. Then, define the thread +function, which accepts three arguments, ``start``, ``end``, and ``arg``, where +the first two delimit the range that the thread operates on and the last is a +pointer to the job's shared state, if any. Prepare the shared state, which is +typically a stack-allocated structure that wraps the required data. Last, call +padata_do_multithreaded(), which will return once the job is finished. + Interface =========