Re: [PATCH RESEND] PCI: dwc: put struct dw_pcie::{ep,pp} into a union to reduce its size

From: "Krzysztof Wilczyński" <kw@linux.com>
To: Alexander Lobakin <alobakin@pm.me>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Jingoo Han <jingoohan1@gmail.com>,
	Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
	Rob Herring <robh@kernel.org>,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND] PCI: dwc: put struct dw_pcie::{ep,pp} into a union to reduce its size
Date: Wed, 24 Mar 2021 02:31:42 +0100	[thread overview]
Message-ID: <YFqWftATEbuxsJbn@rocinante> (raw)
In-Reply-To: <20210312140116.9453-1-alobakin@pm.me>

Hi Alexander,

Thank you for sending the patch over!

> A single dw_pcie entity can't be a root complex and an endpoint at
> the same time.

Nice catch!

A small nitpick: this would be Root Complex and Endpoint, as it's
customary to capitalise these.

Also, if you could capitalise the subject line - it could also perhaps
be simplified to something like, for example:

  Optimize struct dw_pcie to reduce its size

Feel free to ignore both suggestions, as these are just nitpicks.

> We can use this to reduce the size of dw_pcie by 80, from 280 to 200
> bytes (on x32, guess more on x64), by putting the related embedded
> structures (struct pcie_port and struct dw_pcie_ep) into a union.

[...]
> -	struct pcie_port	pp;
> -	struct dw_pcie_ep	ep;
> +	union {
> +		struct pcie_port	pp;
> +		struct dw_pcie_ep	ep;
> +	};
[...]

How did you measure the difference?  Often, people include pahole output
for the "before" and "after", so to speak, to showcase the difference
and/or improvement.  Do you have something like that handy?

Krzysztof