Messages in this thread Patch in this message | | | Subject | Re: [PATCH] clocksource/drivers/tango-xtal: Replace code by clocksource_mmio_init | From | Marc Gonzalez <> | Date | Fri, 13 Nov 2015 13:20:48 +0100 |
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On 13/11/2015 11:58, Daniel Lezcano wrote:
> The current code to initialize, register and read the clocksource is > already factored out in mmio.c via the clocksource_mmio_init function. > > Factor out the code with the clocksource_mmio_init function.
The reason I didn't like clocksource_mmio_init() is because it exports 4 generic accessors.
I guess this function makes more sense when all platforms are using it, in an ARCH_MULTIPLATFORM kernel. (Also the accessors are probably quite small, so the waste is probably minimal.)
In my opinion, defining struct clocksource_mmio with reg "outside" struct clocksource leads to less efficient(1) and less clear(2) code. 1) because of the padding from ____cacheline_aligned 2) because of the container_of() gymnastics
I tried discussing this in March, but it didn't go anywhere. Lemme brush up the patch.
Should the reg field be considered "hot-path data"?
One problem with my patch: if some ports define CLKSRC_MMIO but have lots of static struct clocksource, the extra reg field might waste memory / worsen cache locality?
Also, maybe the fields should be copied in ascending order?
Regards.
diff --git a/drivers/clocksource/mmio.c b/drivers/clocksource/mmio.c index 1593ade2a815..aba5f24ba346 100644 --- a/drivers/clocksource/mmio.c +++ b/drivers/clocksource/mmio.c @@ -10,34 +10,24 @@ #include <linux/init.h> #include <linux/slab.h> -struct clocksource_mmio { - void __iomem *reg; - struct clocksource clksrc; -}; - -static inline struct clocksource_mmio *to_mmio_clksrc(struct clocksource *c) -{ - return container_of(c, struct clocksource_mmio, clksrc); -} - cycle_t clocksource_mmio_readl_up(struct clocksource *c) { - return (cycle_t)readl_relaxed(to_mmio_clksrc(c)->reg); + return (cycle_t)readl_relaxed(c->reg); } cycle_t clocksource_mmio_readl_down(struct clocksource *c) { - return ~(cycle_t)readl_relaxed(to_mmio_clksrc(c)->reg) & c->mask; + return ~(cycle_t)readl_relaxed(c->reg) & c->mask; } cycle_t clocksource_mmio_readw_up(struct clocksource *c) { - return (cycle_t)readw_relaxed(to_mmio_clksrc(c)->reg); + return (cycle_t)readw_relaxed(c->reg); } cycle_t clocksource_mmio_readw_down(struct clocksource *c) { - return ~(cycle_t)readw_relaxed(to_mmio_clksrc(c)->reg) & c->mask; + return ~(cycle_t)readw_relaxed(c->reg) & c->mask; } /** @@ -53,21 +43,21 @@ int __init clocksource_mmio_init(void __iomem *base, const char *name, unsigned long hz, int rating, unsigned bits, cycle_t (*read)(struct clocksource *)) { - struct clocksource_mmio *cs; + struct clocksource *cs; if (bits > 32 || bits < 16) return -EINVAL; - cs = kzalloc(sizeof(struct clocksource_mmio), GFP_KERNEL); + cs = kzalloc(sizeof *cs, GFP_KERNEL); if (!cs) return -ENOMEM; cs->reg = base; - cs->clksrc.name = name; - cs->clksrc.rating = rating; - cs->clksrc.read = read; - cs->clksrc.mask = CLOCKSOURCE_MASK(bits); - cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS; + cs->name = name; + cs->rating = rating; + cs->read = read; + cs->mask = CLOCKSOURCE_MASK(bits); + cs->flags = CLOCK_SOURCE_IS_CONTINUOUS; - return clocksource_register_hz(&cs->clksrc, hz); + return clocksource_register_hz(cs, hz); } diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 278dd279a7a8..03807ca0d54e 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -74,6 +74,9 @@ struct clocksource { u32 shift; u64 max_idle_ns; u32 maxadj; +#ifdef CONFIG_CLKSRC_MMIO + void __iomem *reg; +#endif #ifdef CONFIG_ARCH_CLOCKSOURCE_DATA struct arch_clocksource_data archdata; #endif
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