Though dev->line[] is u8 array we work with it as with u16, u24 or u32
pixels, and also pass it to memcpy() and it's better to align it to at
least 4.
Before the patch, on x86 offsetof(vivi_dev, line) was 1003 and after
patch it is 1004.
There is slight performance increase, but I think is is slight, only
because we start copying not from line[0]:
---- 8< ---- drivers/media/platform/vivi.c
static void vivi_fillbuff(struct vivi_dev *dev, struct vivi_buffer *buf)
{
...
for (h = 0; h < hmax; h++)
memcpy(vbuf + h * wmax * dev->pixelsize,
dev->line + (dev->mv_count % wmax) * dev->pixelsize,
wmax * dev->pixelsize);
before:
# cmdline : /home/kirr/local/perf/bin/perf record -g -a sleep 20
#
# Samples: 49K of event 'cycles'
# Event count (approx.): 16799780016
#
# Overhead Command Shared Object
# ........ ............... ....................
#
27.51% rawv libc-2.13.so [.] __memcpy_ssse3
23.77% vivi-* [kernel.kallsyms] [k] memcpy
9.96% Xorg [unknown] [.] 0xa76f5e12
4.94% vivi-* [vivi] [k] gen_text.constprop.6
4.44% rawv [vivi] [k] gen_twopix
3.17% vivi-* [vivi] [k] vivi_fillbuff
2.45% rawv [vivi] [k] precalculate_line
1.20% swapper [kernel.kallsyms] [k] read_hpet
23.77% vivi-* [kernel.kallsyms] [k] memcpy
|
--- memcpy
|
|--99.28%-- vivi_fillbuff
| vivi_thread
| kthread
| ret_from_kernel_thread
--0.72%-- [...]
after:
# cmdline : /home/kirr/local/perf/bin/perf record -g -a sleep 20
#
# Samples: 49K of event 'cycles'
# Event count (approx.): 16475832370
#
# Overhead Command Shared Object
# ........ ............... ......................
#
29.07% rawv libc-2.13.so [.] __memcpy_ssse3
20.57% vivi-* [kernel.kallsyms] [k] memcpy
10.20% Xorg [unknown] [.] 0xa7301494
5.16% vivi-* [vivi] [k] gen_text.constprop.6
4.43% rawv [vivi] [k] gen_twopix
4.36% vivi-* [vivi] [k] vivi_fillbuff
2.42% rawv [vivi] [k] precalculate_line
1.33% swapper [kernel.kallsyms] [k] read_hpet
Signed-off-by: Kirill Smelkov <kirr@xxxxxxxxxx>
---
drivers/media/platform/vivi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/media/platform/vivi.c b/drivers/media/platform/vivi.c
index cb2337e..ddcc712 100644
--- a/drivers/media/platform/vivi.c
+++ b/drivers/media/platform/vivi.c
@@ -242,7 +242,7 @@ struct vivi_dev {
unsigned int field_count;
u8 bars[9][3];
- u8 line[MAX_WIDTH * 8];
+ u8 line[MAX_WIDTH * 8] __attribute__((__aligned__(4)));
unsigned int pixelsize;
u8 alpha_component;
u32 textfg, textbg;
--
1.8.0.316.g291341c
--
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