linux-kernel - Re: [PATCH v2 0/6] MediaTek IOMMU improve tlb flush performance in map/unmap

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Message-ID: <20201125122719.GB15697@willie-the-truck>
Date:   Wed, 25 Nov 2020 12:27:19 +0000
From:   Will Deacon <will@...nel.org>
To:     Yong Wu <yong.wu@...iatek.com>, robin.murphy@....com
Cc:     Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>, anan.sun@...iatek.com,
        chao.hao@...iatek.com, jun.wen@...iatek.com
Subject: Re: [PATCH v2 0/6] MediaTek IOMMU improve tlb flush performance in
 map/unmap

On Thu, Nov 19, 2020 at 02:18:30PM +0800, Yong Wu wrote:
> This patchset is to improve tlb flushing performance in iommu_map/unmap
> for MediaTek IOMMU.
> 
> For iommu_map, currently MediaTek IOMMU use IO_PGTABLE_QUIRK_TLBI_ON_MAP
> to do tlb_flush for each a memory chunk. this is so unnecessary. we could
> improve it by tlb flushing one time at the end of iommu_map.
> 
> For iommu_unmap, currently we have already improve this performance by
> gather. But the current gather should take care its granule size. if the
> granule size is different, it will do tlb flush and gather again. Our HW
> don't care about granule size. thus I add a flag(granule_ignore) for this
> case.
> 
> After this patchset, we could achieve only tlb flushing once in iommu_map
> and iommu_unmap.
> 
> Regardless of sg, for each a segment, I did a simple test:
>   
>   size = 20 * SZ_1M;
>   /* the worst case, all are 4k mapping. */
>   ret = iommu_map(domain, 0x5bb02000, 0x123f1000, size, IOMMU_READ);
>   iommu_unmap(domain, 0x5bb02000, size);
> 
> This is the comparing time(unit is us):
>               original-time  after-improve
>    map-20M    59943           2347
>    unmap-20M  264             36
> 
> This patchset also flush tlb once in the iommu_map_sg case.
> 
> patch [1/6][2/6][3/6] are for map while the others are for unmap.
> 
> change note:
> v2: Refactor all the code.
>     base on v5.10-rc1.

Robin -- please can you take a look at this series? I'm not sure I'll
have time to get to it at the moment and you understand how this stuff
is supposed to work.

Cheers,

Will