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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 6465EC433FE for ; Wed, 9 Dec 2020 12:12:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3626823B7B for ; Wed, 9 Dec 2020 12:12:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731378AbgLIMMJ (ORCPT ); Wed, 9 Dec 2020 07:12:09 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:8972 "EHLO szxga06-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730385AbgLIMMI (ORCPT ); Wed, 9 Dec 2020 07:12:08 -0500 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4CrbVV5wThzhXm7; Wed, 9 Dec 2020 20:10:58 +0800 (CST) Received: from [127.0.0.1] (10.174.177.9) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.487.0; Wed, 9 Dec 2020 20:11:14 +0800 Subject: Re: [RESEND PATCH v3 3/4] iommu/iova: Flush CPU rcache for when a depot fills To: John Garry , , , CC: , , , References: <1605608734-84416-1-git-send-email-john.garry@huawei.com> <1605608734-84416-4-git-send-email-john.garry@huawei.com> <76e057e3-9db8-21fc-3a8a-b9e924a95cf4@huawei.com> <851ba6cf-8f4c-74dc-3666-ee6d547999d3@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <552fd9c5-d3dd-e1b3-d7e8-2a30904f22c4@huawei.com> Date: Wed, 9 Dec 2020 20:11:13 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <851ba6cf-8f4c-74dc-3666-ee6d547999d3@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.9] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/12/9 19:22, John Garry wrote: > On 09/12/2020 09:13, Leizhen (ThunderTown) wrote: >> >> >> On 2020/11/17 18:25, 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. >>> >>> 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 >>> instabilty 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 >>> Signed-off-by: John Garry > > Thanks for having a look > >>> --- >>>   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 1f3f0f8b12e0..386005055aca 100644 >>> --- a/drivers/iommu/iova.c >>> +++ b/drivers/iommu/iova.c >>> @@ -901,7 +901,6 @@ 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; >>> @@ -923,13 +922,12 @@ 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); >>>           } >>>       } >>>   @@ -938,10 +936,8 @@ 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); >> mag_to_free has been stripped out, that's why lock protection is not required here. >> >>> -    } >>> +    if (!can_insert) >>> +        free_all_cpu_cached_iovas(iovad); >> Lock protection required. > > But we have the per-CPU rcache locking again in free_cpu_cached_iovas() (which is called per-CPU from free_all_cpu_cached_iovas()). > > ok? Or some other lock you mean? Oh, Sorry, think of function free_cpu_cached_iovas() as function free_iova_rcaches(). Reviewed-by: Zhen Lei > > Cheers, > John > >> >>>         return can_insert; >>>   } >>> >> >> . >> > > > . >