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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 55FBDC2D0CF for ; Tue, 24 Dec 2019 11:20:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2835B2053B for ; Tue, 24 Dec 2019 11:20:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1577186434; bh=5op17jsWx2Ma+YJRFe+2cUP0MpYQx2k0rHUHDvFPe2I=; h=To:Subject:Date:From:Cc:In-Reply-To:References:List-ID:From; b=LDduFmbc1FyNnAzKlEO/K2wo5wXZXFaFbkRdwBs8UDSnYl407WIXAmy+zGXuePB5V 7CM5Cp7EuQEHdeLCNE79ftYXd5PXVpVY2IC9fC1lBcvuMgremFmmCaGTpJvM3n1xO8 VMvOJZtQ1ptPGHGkFQYL4RcgfjMcSDW/wzwno+Uw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726222AbfLXLUd (ORCPT ); Tue, 24 Dec 2019 06:20:33 -0500 Received: from inca-roads.misterjones.org ([213.251.177.50]:38264 "EHLO inca-roads.misterjones.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726102AbfLXLUc (ORCPT ); Tue, 24 Dec 2019 06:20:32 -0500 Received: from www-data by cheepnis.misterjones.org with local (Exim 4.80) (envelope-from ) id 1ijiEj-0001Gs-CF; Tue, 24 Dec 2019 12:20:25 +0100 To: Ming Lei Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt X-PHP-Originating-Script: 0:main.inc MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 24 Dec 2019 11:20:25 +0000 From: Marc Zyngier Cc: John Garry , , "chenxiang (M)" , , , , , , , , , Zhang Yi In-Reply-To: <20191224015926.GC13083@ming.t460p> References: <68058fd28c939b8e065524715494de95@www.loen.fr> <687cbcc4-89d9-63ea-a246-ce2abaae501a@huawei.com> <0fd543f8ffd90f90deb691aea1c275b4@www.loen.fr> <20191220233138.GB12403@ming.t460p>

<20191224015926.GC13083@ming.t460p> Message-ID: <7a961950624c414bb9d0c11c914d5c62@www.loen.fr> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/0.7.2 X-SA-Exim-Connect-IP: X-SA-Exim-Rcpt-To: ming.lei@redhat.com, john.garry@huawei.com, tglx@linutronix.de, chenxiang66@hisilicon.com, bigeasy@linutronix.de, linux-kernel@vger.kernel.org, hare@suse.com, hch@lst.de, axboe@kernel.dk, bvanassche@acm.org, peterz@infradead.org, mingo@redhat.com, yi.zhang@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-12-24 01:59, Ming Lei wrote: > On Mon, Dec 23, 2019 at 10:47:07AM +0000, Marc Zyngier wrote: >> On 2019-12-23 10:26, John Garry wrote: >> > > > > > I've also managed to trigger some of them now that I have >> > > > > access to >> > > > > > a decent box with nvme storage. >> > > > > >> > > > > I only have 2x NVMe SSDs when this occurs - I should not be >> > > > > hitting this... >> > > > > >> > > > > Out of curiosity, have you tried >> > > > > > with the SMMU disabled? I'm wondering whether we hit some >> > > > > livelock >> > > > > > condition on unmapping buffers... >> > > > > >> > > > > No, but I can give it a try. Doing that should lower the CPU >> > > > > usage, though, >> > > > > so maybe masks the issue - probably not. >> > > > >> > > > Lots of CPU lockup can is performance issue if there isn't >> > > > obvious bug. >> > > > >> > > > I am wondering if you may explain it a bit why enabling SMMU >> may >> > > > save >> > > > CPU a it? >> > > The other way around. mapping/unmapping IOVAs doesn't comes for >> > > free. >> > > I'm trying to find out whether the NVMe map/unmap patterns >> trigger >> > > something unexpected in the SMMU driver, but that's a very long >> > > shot. >> > >> > So I tested v5.5-rc3 with and without the SMMU enabled, and >> without >> > the SMMU enabled I don't get the lockup. >> >> OK, so my hunch wasn't completely off... At least we have something >> to look into. >> >> [...] >> >> > Obviously this is not conclusive, especially with such limited >> > testing - 5 minute runs each. The CPU load goes up when disabling >> the >> > SMMU, but that could be attributed to extra throughput (1183K -> >> > 1539K) loading. >> > >> > I do notice that since we complete the NVMe request in irq >> context, >> > we also do the DMA unmap, i.e. talk to the SMMU, in the same >> context, >> > which is less than ideal. >> >> It depends on how much overhead invalidating the TLB adds to the >> equation, but we should be able to do some tracing and find out. >> >> > I need to finish for the Christmas break today, so can't check >> this >> > much further ATM. >> >> No worries. May I suggest creating a new thread in the new year, >> maybe >> involving Robin and Will as well? > > Zhang Yi has observed the CPU lockup issue once when running heavy IO > on > single nvme drive, and please CC him if you have new patch to try. On which architecture? John was indicating that this also happen on x86. > Then looks the DMA unmap cost is too big on aarch64 if SMMU is > involved. So far, we don't have any data suggesting that this is actually the case. Also, other workloads (such as networking) do not exhibit this behaviour, while being least as unmap-heavy as NVMe is. If the cross-architecture aspect is confirmed, this points more into the direction of an interaction between the NVMe subsystem and the DMA API more than an architecture-specific problem. Given that we have so far very little data, I'd hold off any conclusion. M. -- Jazz is not dead. It just smells funny...