linux-kernel - Re: [RFC PATCH v3 4/8] vfio/type1: Pre-map more pages than requested in the IOPF handling

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Message-ID: <ba8b6039-d053-2657-ae62-deaa30f452d2@huawei.com>
Date:   Fri, 21 May 2021 14:37:55 +0800
From:   Shenming Lu <lushenming@...wei.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     Cornelia Huck <cohuck@...hat.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>,
        Eric Auger <eric.auger@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <linux-api@...r.kernel.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, <yi.l.liu@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        "Barry Song" <song.bao.hua@...ilicon.com>,
        <wanghaibin.wang@...wei.com>, <yuzenghui@...wei.com>
Subject: Re: [RFC PATCH v3 4/8] vfio/type1: Pre-map more pages than requested
 in the IOPF handling

On 2021/5/19 2:58, Alex Williamson wrote:
> On Fri, 9 Apr 2021 11:44:16 +0800
> Shenming Lu <lushenming@...wei.com> wrote:
> 
>> To optimize for fewer page fault handlings, we can pre-map more pages
>> than requested at once.
>>
>> Note that IOPF_PREMAP_LEN is just an arbitrary value for now, which we
>> could try further tuning.
> 
> I'd prefer that the series introduced full end-to-end functionality
> before trying to improve performance.  The pre-map value seems
> arbitrary here and as noted in the previous patch, the IOMMU API does
> not guarantee unmaps of ranges smaller than the original mapping.  This
> would need to map with single page granularity in order to guarantee
> page granularity at the mmu notifier when the IOMMU supports
> superpages.  Thanks,

Yeah, I will drop this patch in the current stage.

Thanks,
Shenming

> 
> Alex
> 
> .
>