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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 448C1C3276C for ; Fri, 3 Jan 2020 00:46:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 090F521734 for ; Fri, 3 Jan 2020 00:46:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WEesTg6T" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726118AbgACAqu (ORCPT ); Thu, 2 Jan 2020 19:46:50 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:35370 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725872AbgACAqt (ORCPT ); Thu, 2 Jan 2020 19:46:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578012407; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=T55md/uTWdTlXn4xaYfqDWOjh4bsX6MYiWOmj+IeaAQ=; b=WEesTg6TG4+VfXkZtermUMmJFXU+atMF4Ng9D2JaqvekHmSlHyQb7y/zAoXTWsX7Sff6/b ea4dS3E0HzBx12Ep5sQqaupJv7bFGInkqBDAGOmrcUn4qfpo9Hsn6IfT4OIAvuFrOkgDWF NSGBrDIPbU639zZMhIvBFffIw4MmwAQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-170-KKfDAZh1MauqhSTGjygwGQ-1; Thu, 02 Jan 2020 19:46:44 -0500 X-MC-Unique: KKfDAZh1MauqhSTGjygwGQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 782A4107ACC5; Fri, 3 Jan 2020 00:46:42 +0000 (UTC) Received: from ming.t460p (ovpn-8-18.pek2.redhat.com [10.72.8.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E0615271B4; Fri, 3 Jan 2020 00:46:30 +0000 (UTC) Date: Fri, 3 Jan 2020 08:46:25 +0800 From: Ming Lei To: John Garry Cc: Marc Zyngier , tglx@linutronix.de, "chenxiang (M)" , 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, Zhang Yi Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt Message-ID: <20200103004625.GA5219@ming.t460p> References: <0fd543f8ffd90f90deb691aea1c275b4@www.loen.fr> <20191220233138.GB12403@ming.t460p> <20191224015926.GC13083@ming.t460p> <7a961950624c414bb9d0c11c914d5c62@www.loen.fr> <20191225004822.GA12280@ming.t460p> <72a6a738-f04b-3792-627a-fbfcb7b297e1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <72a6a738-f04b-3792-627a-fbfcb7b297e1@huawei.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 02, 2020 at 10:35:31AM +0000, John Garry wrote: > On 25/12/2019 00:48, Ming Lei wrote: > > On Tue, Dec 24, 2019 at 11:20:25AM +0000, Marc Zyngier wrote: > > > 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. > > > > ARM64. > > > > To be honest, I never see such CPU lockup issue on x86 in case of running > > heavy IO on single NVMe drive. > > > > > > > > > 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. > > > > Maybe it is because networking workloads usually completes IO in softirq > > context, instead of hard interrupt context. > > > > > > > > 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. > > > > We can start to collect latency data of dma unmapping vs nvme_irq() > > on both x86 and arm64. > > > > I will see if I can get a such box for collecting the latency data. > > To reiterate what I mentioned before about IOMMU DMA unmap on x86, a key > difference is that by default it uses the non-strict (lazy) mode unmap, i.e. > we unmap in batches. ARM64 uses general default, which is strict mode, i.e. > every unmap results in an IOTLB fluch. > > In my setup, if I switch to lazy unmap (set iommu.strict=0 on cmdline), then > no lockup. > > Are any special IOMMU setups being used for x86, like enabling strict mode? > I don't know... BTW, I have run the test on one 224-core ARM64 with one 32-hw_queue NVMe, the softlock issue can be triggered in one minute. nvme_irq() often takes ~5us to complete on this machine, then there is really risk of cpu lockup when IOPS is > 200K. The soft lockup can be triggered too if 'iommu.strict=0' is passed in, just takes a bit longer by starting more IO jobs. In above test, I submit IO to one single NVMe drive from 4 CPU cores via 8 or 12 jobs(iommu.strict=0), meantime make the nvme interrupt handled just in one dedicated CPU core. Is there lock contention among iommu dma map and unmap callback? Thanks, Ming