Instead of always falling back to memcpy_fromio() for any size, prefer using read{b,w,l}(). When reading struct members it's common to read individual integer variables individually. Going through memcpy_fromio() for each of them poses a high penalty.
Employ a similar trick as __seqprop() by using _Generic() to generate only the specific call based on a type-compatible variable.
For a pariticular i915 workload producing GPU context switches, __get_engine_usage_record() is particularly hot since the engine usage is read from device local memory with dgfx, possibly multiple times since it's racy. Test execution time for this test shows a ~12.5% improvement with DG2:
Before: nrepeats = 1000; min = 7.63243e+06; max = 1.01817e+07; median = 9.52548e+06; var = 526149; After: nrepeats = 1000; min = 7.03402e+06; max = 8.8832e+06; median = 8.33955e+06; var = 333113;
Other things attempted that didn't prove very useful: 1) Change the _Generic() on x86 to just dereference the memory address 2) Change __get_engine_usage_record() to do just 1 read per loop, comparing with the previous value read 3) Change __get_engine_usage_record() to access the fields directly as it was before the conversion to iosys-map
(3) did gave a small improvement (~3%), but doesn't seem to scale well to other similar cases in the driver.
Additional test by Chris Wilson using gem_create from igt with some changes to track object creation time. This happens to accidentally stress this code path:
Pre iosys_map conversion of engine busyness: lmem0: Creating 262144 4KiB objects took 59274.2ms
Unpatched: lmem0: Creating 262144 4KiB objects took 108830.2ms
With readl (this patch): lmem0: Creating 262144 4KiB objects took 61348.6ms
s/readl/READ_ONCE/ lmem0: Creating 262144 4KiB objects took 61333.2ms
So we do take a little bit more time than before the conversion, but that is due to other factors: bringing the READ_ONCE back would be as good as just doing this conversion.
Signed-off-by: Lucas De Marchi lucas.demarchi@intel.com --- include/linux/iosys-map.h | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-)
diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h index e69a002d5aa4..cd28c7a1b79c 100644 --- a/include/linux/iosys-map.h +++ b/include/linux/iosys-map.h @@ -333,6 +333,20 @@ static inline void iosys_map_memset(struct iosys_map *dst, size_t offset, memset(dst->vaddr + offset, value, len); }
+#ifdef CONFIG_64BIT +#define __iosys_map_rd_io_u64_case(val_, vaddr_iomem_) \ + u64: val_ = readq(vaddr_iomem_), +#else +#define __iosys_map_rd_io_u64_case(val_, vaddr_iomem_) +#endif + +#define __iosys_map_rd_io(val__, vaddr_iomem__, type__) _Generic(val__, \ + u8: val__ = readb(vaddr_iomem__), \ + u16: val__ = readw(vaddr_iomem__), \ + u32: val__ = readl(vaddr_iomem__), \ + __iosys_map_rd_io_u64_case(val__, vaddr_iomem__) \ + default: memcpy_fromio(&(val__), vaddr_iomem__, sizeof(val__))) + /** * iosys_map_rd - Read a C-type value from the iosys_map * @@ -346,10 +360,14 @@ static inline void iosys_map_memset(struct iosys_map *dst, size_t offset, * Returns: * The value read from the mapping. */ -#define iosys_map_rd(map__, offset__, type__) ({ \ - type__ val; \ - iosys_map_memcpy_from(&val, map__, offset__, sizeof(val)); \ - val; \ +#define iosys_map_rd(map__, offset__, type__) ({ \ + type__ val; \ + if ((map__)->is_iomem) { \ + __iosys_map_rd_io(val, (map__)->vaddr_iomem + offset__, type__);\ + } else { \ + memcpy(&val, (map__)->vaddr + offset__, sizeof(val)); \ + } \ + val; \ })
/**