linux-kernel - Re: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in non-coherent domains

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Message-ID: <Zk1nleN3kvHTbiov@yzhao56-desk.sh.intel.com>
Date: Wed, 22 May 2024 11:33:41 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: Jason Gunthorpe <jgg@...dia.com>, "Tian, Kevin" <kevin.tian@...el.com>,
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	<baolu.lu@...ux.intel.com>, "Liu, Yi L" <yi.l.liu@...el.com>
Subject: Re: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in
 non-coherent domains

On Tue, May 21, 2024 at 12:19:45PM -0600, Alex Williamson wrote:
> On Tue, 21 May 2024 13:34:00 -0300
> Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > On Tue, May 21, 2024 at 10:21:23AM -0600, Alex Williamson wrote:
 
> Intel folks might be able to comment on the performance hit relative to
> iGPU assignment of denying the device the ability to use no-snoop
> transactions (assuming the device control bit is actually honored).
I don't have direct data for iGPU assignment. But I have a reference
data regarding to virtio GPU.

When backend GPU is iGPU for a virtio GPU, follow non-coherent path could
increase performance up to 20%+ for some platforms.

> The latency of flushing caches on touching no-snoop enable might be
> prohibitive in the latter case.  Thanks,