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Date: Fri, 18 Nov 2022 01:23:36 +0100
From: Andrew Lunn <andrew@lunn.ch>
To: Umang Jain <umang.jain@ideasonboard.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@broadcom.com>,
	Ray Jui <rjui@broadcom.com>, Dan Carpenter <error27@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Dave Stevenson <dave.stevenson@raspberrypi.com>,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	linux-rpi-kernel@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org, linux-staging@lists.linux.dev,
	linux-kernel@vger.kernel.org, kieran.bingham@ideasonboard.com
Subject: Re: [PATCH 2/3] vc04_services: mmal-vchiq: Use bool for
 vchiq_mmal_component.in_use
Message-ID: <Y3bQiDw11t4pRokP@lunn.ch>
References: <20221117160015.344528-1-umang.jain@ideasonboard.com>
 <20221117160015.344528-3-umang.jain@ideasonboard.com>
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In-Reply-To: <20221117160015.344528-3-umang.jain@ideasonboard.com>

>  struct vchiq_mmal_component {
> -	u32 in_use:1;
> +	bool in_use:1;
>  	bool enabled:1;

The patch you referenced says:

+If a structure has many true/false values, consider consolidating them into a
+bitfield with 1 bit members, or using an appropriate fixed width type, such as
+u8.

The code did exactly this, using two bits fields, in one u32. A bool
probably takes up 4 bytes, maybe 8 bytes, so this change probably
doubles the storage size for these two fields. Are these fields on the
hot path, where an extra AND instruction would make a difference?

    Andrew