linux-kernel - Re: [PATCH] iommu/vt-d: Avoid superfluous IOTLB tracking in lazy mode

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Message-ID: <e40cb8c2-1124-4002-75f5-671b4c758b5d@arm.com>
Date:   Mon, 6 Feb 2023 11:05:32 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        stable@...r.kernel.org, Sanjay Kumar <sanjay.k.kumar@...el.com>
Subject: Re: [PATCH] iommu/vt-d: Avoid superfluous IOTLB tracking in lazy mode

On 2023-02-03 23:04, Jacob Pan wrote:
> Intel IOMMU driver implements IOTLB flush queue with domain selective
> or PASID selective invalidations. In this case there's no need to track
> IOVA page range and sync IOTLBs, which may cause significant performance
> hit.
> 
> This patch adds a check to avoid IOVA gather page and IOTLB sync for
> the lazy path.
> 
> The performance difference on Sapphire Rapids 100Gb NIC is improved by
> the following (as measured by iperf send):
> 
> w/o this fix~48 Gbits/s. with this fix ~54 Gbits/s

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Cc: <stable@...r.kernel.org>
> Tested-by: Sanjay Kumar <sanjay.k.kumar@...el.com>
> Signed-off-by: Sanjay Kumar <sanjay.k.kumar@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>   drivers/iommu/intel/iommu.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index b4878c7ac008..705a1c66691a 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4352,7 +4352,13 @@ static size_t intel_iommu_unmap(struct iommu_domain *domain,
>   	if (dmar_domain->max_addr == iova + size)
>   		dmar_domain->max_addr = iova;
>   
> -	iommu_iotlb_gather_add_page(domain, gather, iova, size);
> +	/*
> +	 * We do not use page-selective IOTLB invalidation in flush queue,
> +	 * There is no need to track page and sync iotlb. Domain-selective or
> +	 * PASID-selective validation are used in the flush queue.
> +	 */
> +	if (!gather->queued)
> +		iommu_iotlb_gather_add_page(domain, gather, iova, size);
>   
>   	return size;
>   }