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