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=-1.2 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URG_BIZ,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 C19BAC6778F for ; Mon, 9 Jul 2018 11:07:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 66BD020882 for ; Mon, 9 Jul 2018 11:07:05 +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="lPD/QBZL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 66BD020882 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 S1754481AbeGILHC (ORCPT ); Mon, 9 Jul 2018 07:07:02 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:57050 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754442AbeGILHB (ORCPT ); Mon, 9 Jul 2018 07:07:01 -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-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To: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=ANBm+fYpyBVTcpP5PTbrL8k+EaztPDemNmZXb/ctDys=; b=lPD/QBZLLS8emAx2Qc1ehsHpt9 1O8OJDoTeYVb3Y8o60ZyNYutXNaS4MAch0gci9LukkhktS7SIv/uSMKk58AHIPUlUGy5Z2SjyOLG8 q9R8O21YqrxbmncDV5L2uR+rBM9A/AGAOPJOCqD7r+gUdDlm9JGdtP5hqSLdTxT/xx2r5NBrgJxpF 9uunCJ0iRdGbcM9sxkOAMgOBqgpXNLiJ6q/MoAIcpwI7viiCk6yD+i/JvaxpRM/rcSWv0DG3vxP/p J5OBfFOMp5YTx9kXwZ9FDYVkxcC20IX0umMB6b8ccKSUMUfPVhMGXouelqYUS1x286NjII3TnSPvI 7XJc1kGg==; 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 1fcU0R-0005Nb-9c; Mon, 09 Jul 2018 11:06:59 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BF63620291063; Mon, 9 Jul 2018 13:06:57 +0200 (CEST) Date: Mon, 9 Jul 2018 13:06:57 +0200 From: Peter Zijlstra To: David Woodhouse Cc: "Paul E. McKenney" , mhillenb@amazon.de, linux-kernel Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested Message-ID: <20180709110657.GL2476@hirez.programming.kicks-ass.net> References: <20180706162905.GZ2476@hirez.programming.kicks-ass.net> <20180706171150.GI3593@linux.vnet.ibm.com> <20180709085351.GC2476@hirez.programming.kicks-ass.net> <1531127935.18697.57.camel@infradead.org> <20180709104429.GI2476@hirez.programming.kicks-ass.net> <1531133801.18697.73.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <1531133801.18697.73.camel@infradead.org> 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 Mon, Jul 09, 2018 at 11:56:41AM +0100, David Woodhouse wrote: > > But either proposal is exactly the same in this respect. The whole > > rcu_urgent_qs thing won't be set any earlier either. >=20 > Er.... Marius, our latencies in expand_fdtable() definitely went from > ~10s to well below one second when we just added the rcu_all_qs() into > the loop, didn't they? And that does nothing if !rcu_urgent_qs. Argh I never found that, because obfuscation: ruqp =3D per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu); ... smp_store_release(ruqp, true); I, using git grep "rcu_urgent_qs.*true" only found rcu_request_urgent_qs_task() and sync_sched_exp_handler(). But how come KVM even triggers that case; rcu_implicit_dynticks_qs() is for NOHZ and offline CPUs.