From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932950AbcDEBmW (ORCPT ); Mon, 4 Apr 2016 21:42:22 -0400 Received: from smtp2.ccs.ornl.gov ([160.91.199.39]:46811 "EHLO smtp2.ccs.ornl.gov" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932882AbcDEBmS (ORCPT ); Mon, 4 Apr 2016 21:42:18 -0400 From: James Simmons To: Greg Kroah-Hartman , devel@driverdev.osuosl.org, Andreas Dilger , Oleg Drokin Cc: Linux Kernel Mailing List , Lustre Development List , Ned Bass , James Simmons Subject: [PATCH 12/18] staging: lustre: mdc: document mdc_rpc_lock Date: Mon, 4 Apr 2016 21:36:57 -0400 Message-Id: <1459820223-24754-13-git-send-email-jsimmons@infradead.org> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1459820223-24754-1-git-send-email-jsimmons@infradead.org> References: <1459820223-24754-1-git-send-email-jsimmons@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ned Bass As this lock can be a bottleneck, clarifying why it is needed may be helpful to those working on client performance. Signed-off-by: Ned Bass Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3443 Reviewed-on: http://review.whamcloud.com/6593 Reviewed-by: Andreas Dilger Reviewed-by: Keith Mannthey Signed-off-by: James Simmons --- drivers/staging/lustre/lustre/include/lustre_mdc.h | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-) diff --git a/drivers/staging/lustre/lustre/include/lustre_mdc.h b/drivers/staging/lustre/lustre/include/lustre_mdc.h index df94f9f..9e54790 100644 --- a/drivers/staging/lustre/lustre/include/lustre_mdc.h +++ b/drivers/staging/lustre/lustre/include/lustre_mdc.h @@ -64,9 +64,27 @@ struct obd_export; struct ptlrpc_request; struct obd_device; +/** + * Serializes in-flight MDT-modifying RPC requests to preserve idempotency. + * + * This mutex is used to implement execute-once semantics on the MDT. + * The MDT stores the last transaction ID and result for every client in + * its last_rcvd file. If the client doesn't get a reply, it can safely + * resend the request and the MDT will reconstruct the reply being aware + * that the request has already been executed. Without this lock, + * execution status of concurrent in-flight requests would be + * overwritten. + * + * This design limits the extent to which we can keep a full pipeline of + * in-flight requests from a single client. This limitation could be + * overcome by allowing multiple slots per client in the last_rcvd file. + */ struct mdc_rpc_lock { + /** Lock protecting in-flight RPC concurrency. */ struct mutex rpcl_mutex; + /** Intent associated with currently executing request. */ struct lookup_intent *rpcl_it; + /** Used for MDS/RPC load testing purposes. */ int rpcl_fakes; }; -- 1.7.1