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

From: Jason Gunthorpe <jgg@nvidia.com>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>,
	Christoph Hellwig <hch@infradead.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>, Vinod Koul <vkoul@kernel.org>,
	Eric Auger <eric.auger@redhat.com>, Liu Yi L <yi.l.liu@intel.com>,
	Jacob jun Pan <jacob.jun.pan@intel.com>,
	Zhangfei Gao <zhangfei.gao@linaro.org>,
	Zhu Tony <tony.zhu@intel.com>,
	iommu@lists.linux.dev, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v12 07/17] iommu: Try to allocate blocking domain when probing device
Date: Fri, 26 Aug 2022 11:52:31 -0300	[thread overview]
Message-ID: <YwjeL2SVmdRpoWb6@nvidia.com> (raw)
In-Reply-To: <20220826121141.50743-8-baolu.lu@linux.intel.com>

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@linux.intel.com>
> Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
> Tested-by: Tony Zhu <tony.zhu@intel.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?

Jason