Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [RFC PATCH v3 4/8] vfio/type1: Pre-map more pages than requested
 in the IOPF handling
To:     Alex Williamson <alex.williamson@redhat.com>
CC:     Cornelia Huck <cohuck@redhat.com>, Will Deacon <will@kernel.org>,
        "Robin Murphy" <robin.murphy@arm.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Jean-Philippe Brucker" <jean-philippe@linaro.org>,
        Eric Auger <eric.auger@redhat.com>, <kvm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <iommu@lists.linux-foundation.org>, <linux-api@vger.kernel.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>, <yi.l.liu@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        "Barry Song" <song.bao.hua@hisilicon.com>,
        <wanghaibin.wang@huawei.com>, <yuzenghui@huawei.com>
References: <20210409034420.1799-1-lushenming@huawei.com>
 <20210409034420.1799-5-lushenming@huawei.com>
 <20210518125826.7ba38b78.alex.williamson@redhat.com>
From:   Shenming Lu <lushenming@huawei.com>
Message-ID: <ba8b6039-d053-2657-ae62-deaa30f452d2@huawei.com>
Date:   Fri, 21 May 2021 14:37:55 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.2.2
MIME-Version: 1.0
In-Reply-To: <20210518125826.7ba38b78.alex.williamson@redhat.com>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2021/5/19 2:58, Alex Williamson wrote:
> On Fri, 9 Apr 2021 11:44:16 +0800
> Shenming Lu <lushenming@huawei.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
> 
> .
>