On Fri, Jun 17, 2022 at 01:52:03AM -0700, Lucas De Marchi wrote:
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:
- Change the _Generic() on x86 to just dereference the memory address
- 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.
v2:
- Remove default from _Generic() - callers wanting to read more
than u64 should use iosys_map_memcpy_from()
- Add READ_ONCE() cases dereferencing the pointer when using system
memory
Signed-off-by: Lucas De Marchi lucas.demarchi@intel.com Reviewed-by: Christian König christian.koenig@amd.com # v1
include/linux/iosys-map.h | 45 +++++++++++++++++++++++++++++++-------- 1 file changed, 36 insertions(+), 9 deletions(-)
diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h index 4b8406ee8bc4..f59dd00ed202 100644 --- a/include/linux/iosys-map.h +++ b/include/linux/iosys-map.h @@ -6,6 +6,7 @@ #ifndef __IOSYS_MAP_H__ #define __IOSYS_MAP_H__
+#include <linux/compiler_types.h> #include <linux/io.h> #include <linux/string.h>
@@ -333,6 +334,26 @@ 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_) \
- u64: memcpy_fromio(&(val_), vaddr_iomem__, sizeof(u64))
I tested io/sys and forgot again to test it for 32-bit :(. This should fix the build for 32-bits:
diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h index 580e14cd360c..f8bc052f8975 100644 --- a/include/linux/iosys-map.h +++ b/include/linux/iosys-map.h @@ -341,7 +341,7 @@ static inline void iosys_map_memset(struct iosys_map *dst, size_t offset, u64: writeq(val_, vaddr_iomem_) #else #define __iosys_map_rd_io_u64_case(val_, vaddr_iomem_) \ - u64: memcpy_fromio(&(val_), vaddr_iomem__, sizeof(u64)) + u64: memcpy_fromio(&(val_), vaddr_iomem_, sizeof(u64)) #define __iosys_map_wr_io_u64_case(val_, vaddr_iomem_) \ u64: memcpy_toio(vaddr_iomem_, &(val_), sizeof(u64)) #endif
Lucas De Marchi