[PATCH] clocksource: Store reg field within struct clocksource

Marc Gonzalez
2015-11-18T13:43:51Z

Since 'struct clocksource' is ____cacheline_aligned, gcc must insert
a lot of padding between reg and clksrc in 'struct clocksource_mmio'
(for example, L1_CACHE_BYTES = 64 on ARMv7).

Storing reg within 'struct clocksource' removes unnecessary padding,
and reg can then be grouped with other hot data. A nice side-effect
of this patch is making container_of() unnecessary, which makes the
code a bit simpler.

On 32-bit platforms, reg fits in the padding between read and mask,
meaning no downside from storing it there.

0 4 8
+----------------+----------------+
| read | pad/reg |
+----------------+----------------+
| mask |
+----------------+----------------+
| mult | shift |
+----------------+----------------+
| max_idle_ns |
+----------------+----------------+

On 64-bit platforms, placing reg between read and mask changes the
layout, moving max_idle_ns to offset +32 instead of +24.

0 4 8
+----------------+----------------+
| read |
+----------------+----------------+
| reg |
+----------------+----------------+
| mask |
+----------------+----------------+
| mult | shift |
+----------------+----------------+
| max_idle_ns |
+----------------+----------------+

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
---
drivers/clocksource/mmio.c | 36 +++++++++++++-----------------------
include/linux/clocksource.h | 3 +++
2 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/drivers/clocksource/mmio.c b/drivers/clocksource/mmio.c
index 1593ade2a815..c28fc6ef63ef 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->read = read;
+ cs->reg = base;
+ cs->name = name;
+ cs->rating = rating;
+ 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..50725fd23ab0 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -69,6 +69,9 @@ struct clocksource {
* clocksource itself is cacheline aligned.
*/
cycle_t (*read)(struct clocksource *cs);
+#ifdef CONFIG_CLKSRC_MMIO
+ void __iomem *reg;
+#endif
cycle_t mask;
u32 mult;
u32 shift;
--
2.4.5