Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()

From: Jason Gunthorpe <jgg@nvidia.com>
To: David Laight <David.Laight@aculab.com>
Cc: 'Niklas Schnelle' <schnelle@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
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	Will Deacon <will@kernel.org>
Subject: Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()
Date: Fri, 23 Feb 2024 09:03:08 -0400	[thread overview]
Message-ID: <20240223130308.GF13330@nvidia.com> (raw)
In-Reply-To: <d4150af74d7c45b79c770cd1c5d8eed7@AcuMS.aculab.com>

On Fri, Feb 23, 2024 at 12:19:24PM +0000, David Laight wrote:

> Since writes get 'posted' all over the place.
> How many writes do you need to do before write-combining makes a
> difference?

The issue is that the HW can optimize if the entire transaction is
presented in one TLP, if it has to reassemble the transaction it takes
a big slow path hit.

Jason