linux-kernel - Re: [PATCH v12 07/17] iommu: Try to allocate blocking domain when probing device

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Date:   Mon, 29 Aug 2022 11:40:24 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 07/17] iommu: Try to allocate blocking domain when
 probing device

On 2022/8/26 22:52, Jason Gunthorpe wrote:
> On Fri, Aug 26, 2022 at 08:11:31PM +0800, Lu Baolu wrote:
>> Allocate the blocking domain when probing devices if the driver supports
>> blocking domain allocation. Otherwise, revert to the previous behavior,
>> that is, use UNMANAGED domain instead when the blocking domain is needed.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> Tested-by: Zhangfei Gao<zhangfei.gao@...aro.org>
>> Tested-by: Tony Zhu<tony.zhu@...el.com>
>> ---
>>   drivers/iommu/iommu.c | 29 +++++++++++++++++------------
>>   1 file changed, 17 insertions(+), 12 deletions(-)
> This seems like a lot of overhead to allocate these things for every
> group?
> 
> Why not add a simple refcount on the blocking domain instead and
> allocate the domain on the pasid attach like we do for ownership?

I am working towards implementing static instance of blocking domain for
each IOMMU driver, and then, there's no much overhead to allocate it in
the probing device path.

Best regards,
baolu