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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 0B62FC433E0 for ; Fri, 15 Jan 2021 17:33:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D18B3206D4 for ; Fri, 15 Jan 2021 17:33:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730304AbhAORct (ORCPT ); Fri, 15 Jan 2021 12:32:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726151AbhAORcq (ORCPT ); Fri, 15 Jan 2021 12:32:46 -0500 Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 345CAC061757 for ; Fri, 15 Jan 2021 09:32:06 -0800 (PST) Received: by mail-wm1-x32d.google.com with SMTP id 190so8114241wmz.0 for ; Fri, 15 Jan 2021 09:32:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=oqv7QfAT5DV1oDIfe2USMaVgNotzEPUcDQhlXDEIEFM=; b=tA0U7STuqJQUC6bVDAU+1tXQBPtKRxaDrnrV3RiBkr1xjjQvghZpIegxyTvyC+ZHo2 D+aTy3/XYFVj9yALy8tD/4DBZO3733PxQGULqpcEfDdldLum+Yr3SqUpqdkQMG7C4hp+ T1aBMK3dTnsyvWALdO2zK9LNISK3VBs5+KSCpi5+a50mKLKe5E2MbVzOXt6Y7JbKHRpE ix5xhGzoYzO/BM28Vp1UrRcNJBIRJRXxAlZXCRBtE551CteQg0wasrQajVM5gdY9DHvH Vt7f6mxi7cuco9irVMI3aU0CKAili3fvSzOJQdBNCsIRQSjzVyitWvG/kmUJQf9pr3q4 SCLQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=oqv7QfAT5DV1oDIfe2USMaVgNotzEPUcDQhlXDEIEFM=; b=SqYrmQnHENSnhyyaa/EBBPnPSlTS6dUPOFMBNKHfwE5TAGZGdPb5GURy50L0aeeSVd T/Gy/fq8MA8U1xtb+2dp26HRp2NYiWlMPfZOs0B6rdejz1qI8ceTdWKP44RuhRS4PtAB n/ybqQHqHsBMsiH07DYyYbDOjnYFc0n5j9I/2r73+iRkUDMKf9WEYBwDmXSupNz9tNFM Dg8HeYQUNrgglmD4+uC6uWqMcRsv/OdrZPtHmX+wnkt2CnMLdi3QdpoNfkSCTiGr3Mk0 dyltQUMnV1/frIM1UcH3mRtA/fnBJ9NdZWrew2udvPZlFrQkynNJiOhkHdxa+xxHzvQk nNNw== X-Gm-Message-State: AOAM531VTHzQDTdfbtxHGXLau7ZcATZRQDDHd1i44KBSJ9ToP79Pr3ce NWOXlF+zxUvmouDURohou7X3gg== X-Google-Smtp-Source: ABdhPJwMBg+tI2QTs3jPXfHCQqY9HkrW2RbjXihxLuD3aDagCLJVMbSLR90NBqXSVgL1B+J6Tdv19Q== X-Received: by 2002:a05:600c:2158:: with SMTP id v24mr9484177wml.129.1610731924845; Fri, 15 Jan 2021 09:32:04 -0800 (PST) Received: from larix.localdomain ([2001:1715:4e26:a7e0:ed35:e18a:5e36:8c84]) by smtp.gmail.com with ESMTPSA id v7sm13689605wma.26.2021.01.15.09.32.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Jan 2021 09:32:04 -0800 (PST) Date: Fri, 15 Jan 2021 18:32:49 +0100 From: Jean-Philippe Brucker To: John Garry Cc: joro@8bytes.org, will@kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, iommu@lists.linux-foundation.org, robin.murphy@arm.com Subject: Re: [PATCH v4 3/3] iommu/iova: Flush CPU rcache for when a depot fills Message-ID: References: <1607538189-237944-1-git-send-email-john.garry@huawei.com> <1607538189-237944-4-git-send-email-john.garry@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1607538189-237944-4-git-send-email-john.garry@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 10, 2020 at 02:23:09AM +0800, John Garry wrote: > Leizhen reported some time ago that IOVA performance may degrade over time > [0], but unfortunately his solution to fix this problem was not given > attention. > > To summarize, the issue is that as time goes by, the CPU rcache and depot > rcache continue to grow. As such, IOVA RB tree access time also continues > to grow. > > At a certain point, a depot may become full, and also some CPU rcaches may > also be full when inserting another IOVA is attempted. For this scenario, > currently the "loaded" CPU rcache is freed and a new one is created. This > freeing means that many IOVAs in the RB tree need to be freed, which > makes IO throughput performance fall off a cliff in some storage scenarios: > > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6314MB/0KB/0KB /s] [1616K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [5669MB/0KB/0KB /s] [1451K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6031MB/0KB/0KB /s] [1544K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6673MB/0KB/0KB /s] [1708K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6705MB/0KB/0KB /s] [1717K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6031MB/0KB/0KB /s] [1544K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6761MB/0KB/0KB /s] [1731K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6705MB/0KB/0KB /s] [1717K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6685MB/0KB/0KB /s] [1711K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6178MB/0KB/0KB /s] [1582K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6731MB/0KB/0KB /s] [1723K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [2387MB/0KB/0KB /s] [611K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [2689MB/0KB/0KB /s] [688K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [2278MB/0KB/0KB /s] [583K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [1288MB/0KB/0KB /s] [330K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [1632MB/0KB/0KB /s] [418K/0/0 iops] > Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [1765MB/0KB/0KB /s] [452K/0/0 iops] > > And continue in this fashion, without recovering. Note that in this > example it was required to wait 16 hours for this to occur. Also note that > IO throughput also becomes gradually becomes more unstable leading up to > this point. > > This problem is only seen for non-strict mode. For strict mode, the rcaches > stay quite compact. It would be good to understand why the rcache doesn't stabilize. Could be a bug, or just need some tuning In strict mode, if a driver does Alloc-Free-Alloc and the first alloc misses the rcache, the second allocation hits it. The same sequence in non-strict mode misses the cache twice, because the IOVA is added to the flush queue on Free. So rather than AFAFAF.. we get AAA..FFF.., only once the fq_timer triggers or the FQ is full. Interestingly the FQ size is 2x IOVA_MAG_SIZE, so we could allocate 2 magazines worth of fresh IOVAs before alloc starts hitting the cache. If a job allocates more than that, some magazines are going to the depot, and with multi-CPU jobs those will get used on other CPUs during the next alloc bursts, causing the progressive increase in rcache consumption. I wonder if setting IOVA_MAG_SIZE > IOVA_FQ_SIZE helps reuse of IOVAs? Then again I haven't worked out the details, might be entirely wrong. I'll have another look next week. Thanks, Jean > As a solution to this issue, judge that the IOVA caches have grown too big > when cached magazines need to be free, and just flush all the CPUs rcaches > instead. > > The depot rcaches, however, are not flushed, as they can be used to > immediately replenish active CPUs. > > In future, some IOVA compaction could be implemented to solve the > instability issue, which I figure could be quite complex to implement. > > [0] https://lore.kernel.org/linux-iommu/20190815121104.29140-3-thunder.leizhen@huawei.com/ > > Analyzed-by: Zhen Lei > Reported-by: Xiang Chen > Tested-by: Xiang Chen > Signed-off-by: John Garry > Reviewed-by: Zhen Lei > --- > drivers/iommu/iova.c | 16 ++++++---------- > 1 file changed, 6 insertions(+), 10 deletions(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index 732ee687e0e2..39b7488de8bb 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -841,7 +841,6 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > struct iova_rcache *rcache, > unsigned long iova_pfn) > { > - struct iova_magazine *mag_to_free = NULL; > struct iova_cpu_rcache *cpu_rcache; > bool can_insert = false; > unsigned long flags; > @@ -863,13 +862,12 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > if (cpu_rcache->loaded) > rcache->depot[rcache->depot_size++] = > cpu_rcache->loaded; > - } else { > - mag_to_free = cpu_rcache->loaded; > + can_insert = true; > + cpu_rcache->loaded = new_mag; > } > spin_unlock(&rcache->lock); > - > - cpu_rcache->loaded = new_mag; > - can_insert = true; > + if (!can_insert) > + iova_magazine_free(new_mag); > } > } > > @@ -878,10 +876,8 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > > spin_unlock_irqrestore(&cpu_rcache->lock, flags); > > - if (mag_to_free) { > - iova_magazine_free_pfns(mag_to_free, iovad); > - iova_magazine_free(mag_to_free); > - } > + if (!can_insert) > + free_all_cpu_cached_iovas(iovad); > > return can_insert; > } > -- > 2.26.2 > > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu