From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752363AbeEOIfi (ORCPT ); Tue, 15 May 2018 04:35:38 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49828 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752044AbeEOIfg (ORCPT ); Tue, 15 May 2018 04:35:36 -0400 Date: Tue, 15 May 2018 10:35:25 +0200 From: Peter Zijlstra To: Waiman Long Cc: Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Davidlohr Bueso , "Theodore Y. Ts'o" , Oleg Nesterov , Amir Goldstein , Jan Kara Subject: Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release() Message-ID: <20180515083525.GV12217@hirez.programming.kicks-ass.net> References: <1526326267-22501-1-git-send-email-longman@redhat.com> <1526326267-22501-3-git-send-email-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1526326267-22501-3-git-send-email-longman@redhat.com> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire(). > During that period, the rwsem is now marked as writer-owned with no > optimistic spinning. This does not explain the problem sufficiently to even begin considering if the proposed solution is sensible.