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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham 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 2E01CC04ABB for ; Tue, 11 Sep 2018 19:38:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D64EB206BB for ; Tue, 11 Sep 2018 19:38:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ILAgWc4j" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D64EB206BB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728139AbeILAjQ (ORCPT ); Tue, 11 Sep 2018 20:39:16 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:36296 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726689AbeILAjQ (ORCPT ); Tue, 11 Sep 2018 20:39:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=kJYhv21CnZKsfBNNf+sS/5xKXuLQo3CAA080Yftlf5M=; b=ILAgWc4jpLoHOB6N8FuboCFZz ax08LVw8T2wmgQ6vDuW0d+sQC/bvMfC+aDsjZTxew+cFLprToZ6s2f4ftLEIXgoXhuXBM9NR7otsV 7t5PaGjghOB7o0Yf8bq+hFJ2MkhJt2zh62Lx9dSgDGM4vyTnETka7mSmXs0ttduswxO+tJrIPBrmc AZE6wEwEtflab8l36oG9MkwfmU1TaOXxTXSFwej2jocvmBcZgkLL2Iwrp8DVqnwy8heZ6tSAE43Jk 72IEw1gdTAD+nio5G2jYTERIQ2YtIKMshd5bXx0iAgxNOUhhrEcu5UyY8hEqG6ITYl7zc6T15EhH2 Nt7WAhzIg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fzoUU-00038X-Qb; Tue, 11 Sep 2018 19:38:26 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2B16C202C1A00; Tue, 11 Sep 2018 21:38:24 +0200 (CEST) Date: Tue, 11 Sep 2018 21:38:24 +0200 From: Peter Zijlstra To: Davidlohr Bueso Cc: Waiman Long , Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org Subject: Re: [PATCH] locking/rwsem: Make owner store task pointer of last owning reader Message-ID: <20180911193824.GW24106@hirez.programming.kicks-ass.net> References: <1536265114-10842-1-git-send-email-longman@redhat.com> <20180910093156.GS24082@hirez.programming.kicks-ass.net> <20180911192122.GD3902@linux-r8p5> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180911192122.GD3902@linux-r8p5> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 11, 2018 at 12:21:22PM -0700, Davidlohr Bueso wrote: > On Mon, 10 Sep 2018, Peter Zijlstra wrote: > > > [ RT has something along those lines, and I have half a patch that > > starts doing that too, but I never found enough time to really work on > > it :-( ] > > But don't rt rwsems act pretty much like a regular mutex in that it only > allows readers to nest, not share the lock because of priority inversion > scenarios. > > Also, wrt rtmutex, will that top-spinner thing ever make it in? Nah, tglx rewrote that a while ago. It's something semi clever now. Lemme see if I can find the patch. https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/kernel/locking/rwsem-rt.c?h=linux-4.18.y-rt&id=1a42d0b3c3f34895cb5d63e1cd2be02f6077919b