linux-kernel - Re: [PATCH v5 0/6] Add Tegra241 (Grace) CMDQV Support (part 1/2)

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Date: Mon, 15 Apr 2024 14:14:26 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	Jerry Snitselaar <jsnitsel@...hat.com>
Subject: Re: [PATCH v5 0/6] Add Tegra241 (Grace) CMDQV Support (part 1/2)

On Fri, Apr 12, 2024 at 08:43:48PM -0700, Nicolin Chen wrote:

> The user-space support is to provide uAPIs (via IOMMUFD) for hypervisors
> in user space to passthrough VCMDQs to VMs, allowing these VMs to access
> the VCMDQs directly without trappings, i.e. no VM Exits. This gives huge
> performance improvements: 70% to 90% reductions of TLB invalidation time
> were measured by various DMA unmap tests running in a guest OS, compared
> to a nested SMMU CMDQ (with trappings).

So everyone is on the same page, this is the primary point of this
series. The huge speed up of in-VM performance is necessary for the
workloads this chip is expected to be running. This series is unique
from all the rest because it runs inside a VM, often in the from of a
distro release.

It doesn't need the other series or it's own part 2 as it entirely
stands alone on bare metal hardware or on top of commercial VM cloud
instances runing who-knows-what in their hypervisors.

The other parts are substantially about enabling qemu and the open
ecosystem to have fully functional vSMMU3 virtualization.

Jason