linux-kernel - Re: [PATCH v2 0/2] iommu/iova: enhance the rcache optimization

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Date:   Fri, 23 Aug 2019 16:15:00 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>,
        John Garry <john.garry@...wei.com>,
        "Robin Murphy" <robin.murphy@....com>,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Omer Peleg <omer@...technion.ac.il>,
        Adam Morrison <mad@...technion.ac.il>,
        Shaohua Li <shli@...com>, Ben Serebrin <serebrin@...gle.com>,
        David Woodhouse <David.Woodhouse@...el.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] iommu/iova: enhance the rcache optimization

Hi all,
  Can anyone help review it?


On 2019/8/15 20:11, Zhen Lei wrote:
> v1 --> v2
> 1. I did not chagne the patches but added this cover-letter.
> 2. Add a batch of reviewers base on
>    9257b4a206fc ("iommu/iova: introduce per-cpu caching to iova allocation")
> 3. I described the problem I met in patch 2, but I hope below brief description
>    can help people to quickly understand.
>    Suppose there are six rcache sizes, each size can maximum hold 10000 IOVAs.
>    --------------------------------------------
>    |  4K   |  8K  | 16K  |  32K | 64K  | 128K |
>    --------------------------------------------
>    | 10000 | 9000 | 8500 | 8600 | 9200 | 7000 |
>    --------------------------------------------
>    As the above map displayed, the whole rcache buffered too many IOVAs. Now, the
>    worst case can be coming, suppose we need 20000 4K IOVAs at one time. That means
>    10000 IOVAs can be allocated from rcache, but another 10000 IOVAs should be 
>    allocated from RB tree base on alloc_iova() function. But the RB tree currently
>    have at least (9000 + 8500 + 8600 + 9200 + 7000) = 42300 nodes. The average speed
>    of RB tree traverse will be very slow. For my test scenario, the 4K size IOVAs are
>    frequently used, but others are not. So similarly, when the 20000 4K IOVAs are
>    continuous freed, the first 10000 IOVAs can be quickly buffered, but the other
>    10000 IOVAs can not.
> 
> Zhen Lei (2):
>   iommu/iova: introduce iova_magazine_compact_pfns()
>   iommu/iova: enhance the rcache optimization
> 
>  drivers/iommu/iova.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++----
>  include/linux/iova.h |   1 +
>  2 files changed, 95 insertions(+), 6 deletions(-)
>