On Wed, 18 Apr 2018, Joe Perches wrote:
> On Tue, 2018-04-17 at 17:07 +0800, [email protected] wrote: > > Hi julia, > > > > On 2018-04-15 05:19 AM, Julia Lawall wrote: > > > On Wed, 11 Apr 2018, Joe Perches wrote: > > > > > > > On Thu, 2018-04-12 at 08:22 +0200, Julia Lawall wrote: > > > > > On Wed, 11 Apr 2018, Joe Perches wrote: > > > > > > On Wed, 2018-04-11 at 09:29 -0700, Andrew Morton wrote: > > > > > > > We already have some 500 bools-in-structs > > > > > > > > > > > > I got at least triple that only in include/ > > > > > > so I expect there are at probably an order > > > > > > of magnitude more than 500 in the kernel. > > > > > > > > > > > > I suppose some cocci script could count the > > > > > > actual number of instances. A regex can not. > > > > > > > > > > I got 12667. > > > > > > > > Could you please post the cocci script? > > > > > > > > > I'm not sure to understand the issue. Will using a bitfield help if > > > > > there > > > > > are no other bitfields in the structure? > > > > > > > > IMO, not really. > > > > > > > > The primary issue is described by Linus here: > > > > https://lkml.org/lkml/2017/11/21/384 > > > > > > > > I personally do not find a significant issue with > > > > uncontrolled sizes of bool in kernel structs as > > > > all of the kernel structs are transitory and not > > > > written out to storage. > > > > > > > > I suppose bool bitfields are also OK, but for the > > > > RMW required. > > > > > > > > Using unsigned int :1 bitfield instead of bool :1 > > > > has the negative of truncation so that the uint > > > > has to be set with !! instead of a simple assign. > > > > > > At least with gcc 5.4.0, a number of structures become larger with > > > unsigned int :1. bool:1 seems to mostly solve this problem. The > > > structure > > > ichx_desc, defined in drivers/gpio/gpio-ich.c seems to become larger > > > with > > > both approaches. > > > > [ZJ] Hopefully, this could make it better in your environment. > > IMHO, this is just for double check. > > I doubt this is actually better or smaller code. > > Check the actual object code using objdump and the > struct alignment using pahole. I didn't have a chance to try it, but it looks quite likely to result in a smaller data structure based on the other examples that I looked at. julia > > > diff --git a/drivers/gpio/gpio-ich.c b/drivers/gpio/gpio-ich.c > > index 4f6d643..b46e170 100644 > > --- a/drivers/gpio/gpio-ich.c > > +++ b/drivers/gpio/gpio-ich.c > > @@ -70,6 +70,18 @@ static const u8 avoton_reglen[3] = { > > #define ICHX_READ(reg, base_res) inl((reg) + (base_res)->start) > > > > struct ichx_desc { > > + /* GPO_BLINK is available on this chipset */ > > + bool uses_gpe0:1; > > + > > + /* Whether the chipset has GPIO in GPE0_STS in the PM IO region > > */ > > + bool uses_gpe0:1; > > + > > + /* > > + * Some chipsets don't let reading output values on GPIO_LVL > > register > > + * this option allows driver caching written output values > > + */ > > + bool use_outlvl_cache:1; > > + > > /* Max GPIO pins the chipset can have */ > > uint ngpio; > > > > @@ -77,24 +89,12 @@ struct ichx_desc { > > const u8 (*regs)[3]; > > const u8 *reglen; > > > > - /* GPO_BLINK is available on this chipset */ > > - bool have_blink; > > - > > - /* Whether the chipset has GPIO in GPE0_STS in the PM IO region > > */ > > - bool uses_gpe0; > > - > > /* USE_SEL is bogus on some chipsets, eg 3100 */ > > u32 use_sel_ignore[3]; > > > > /* Some chipsets have quirks, let these use their own > > request/get */ > > int (*request)(struct gpio_chip *chip, unsigned offset); > > int (*get)(struct gpio_chip *chip, unsigned offset); > > - > > - /* > > - * Some chipsets don't let reading output values on GPIO_LVL > > register > > - * this option allows driver caching written output values > > - */ > > - bool use_outlvl_cache; > > }; > > > > > > ZJ >
