Re: [PATCH v2] loongarch/mm: disable WUC for pgprot_writecombine as same as ioremap_wc

[Sui Jingfeng]

On 2024/12/19 12:49, Icenowy Zheng wrote:
> 在 2024-12-19星期四的 10:54 +0800，Sui Jingfeng写道：
> > On 2024/12/18 20:43, Icenowy Zheng wrote:
> > > For the fact of drm/ast's dramatical drop, it's because write to
> > > the
> > > framebuffer can no longer be reordered.
> >
> > No, your understanding is wrong, very very wrong and a big wrong.
> >
> > It's not because it can't reorder the write. Rather, it's because
> > that the CPU can't do write gathering and can't do burst write any
> > more.
> Write gathering is a kind of write reordering,


No, your understanding is broken.

Write gathering *isn't* a kind of write reordering.
Its doesn't have to reorder, it just cache the write operation with
the CPU's write buffer.


> comparing to strongly
> ordered writing (which is literally one byte per write).
>
> > So do you still think your patch is harmless?
> Well, I said that performance w/o correctness is meaningless.


The point is that Write-Combine on drm/ast will get both correctness and performance.


> >
--
Best regards,
Sui