iosys-map: Add per-word read

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.

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
v3:
  - Fix precedence issue when casting inside READ_ONCE(). By not using ()
    around vaddr__ the offset was not part of the cast, but rather added
    to it, producing a wrong address
  - Remove compiletime_assert() as READ_ONCE() already contains it

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com> # v1
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220628191016.3899428-1-lucas.demarchi@intel.com
This commit is contained in:
Lucas De Marchi 2022-06-28 12:10:15 -07:00
parent 9db35bb349
commit 5f278dbd54

View File

@ -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 +334,23 @@ 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))
#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__))
#define __iosys_map_rd_sys(val__, vaddr__, type__) \
val__ = READ_ONCE(*(type__ *)(vaddr__))
/**
* iosys_map_rd - Read a C-type value from the iosys_map
*
@ -340,16 +358,21 @@ static inline void iosys_map_memset(struct iosys_map *dst, size_t offset,
* @offset__: The offset from which to read
* @type__: Type of the value being read
*
* Read a C type value from iosys_map, handling possible un-aligned accesses to
* the mapping.
* Read a C type value (u8, u16, u32 and u64) from iosys_map. For other types or
* if pointer may be unaligned (and problematic for the architecture supported),
* use iosys_map_memcpy_from().
*
* 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 { \
__iosys_map_rd_sys(val, (map__)->vaddr + (offset__), type__); \
} \
val; \
})
/**
@ -379,9 +402,10 @@ static inline void iosys_map_memset(struct iosys_map *dst, size_t offset,
*
* Read a value from iosys_map considering its layout is described by a C struct
* starting at @struct_offset__. The field offset and size is calculated and its
* value read handling possible un-aligned memory accesses. For example: suppose
* there is a @struct foo defined as below and the value ``foo.field2.inner2``
* needs to be read from the iosys_map:
* value read. If the field access would incur in un-aligned access, then either
* iosys_map_memcpy_from() needs to be used or the architecture must support it.
* For example: suppose there is a @struct foo defined as below and the value
* ``foo.field2.inner2`` needs to be read from the iosys_map:
*
* .. code-block:: c
*