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| /linux/drivers/gpu/drm/i915/gem/selftests/ |
| H A D | i915_gem_coherency.c | diff 40b399000665ee154927a8e0d7b0c7e7505bbaef Sun Dec 03 14:29:43 CET 2023 Zhao Liu <zhao1.liu@intel.com> drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_coherency.c
The use of kmap_atomic() is being deprecated in favor of
kmap_local_page()[1], and this patch converts the call from
kmap_atomic() to kmap_local_page().
The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration)..
With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults or preemption disables.
In drm/i915/gem/selftests/i915_gem_coherency.c, functions cpu_set()
and cpu_get() mainly uses mapping to flush cache and assign the value.
There're 2 reasons why cpu_set() and cpu_get() don't need to disable
pagefaults and preemption for mapping:
1. The flush operation is safe. cpu_set() and cpu_get() call
drm_clflush_virt_range() to use CLFLUSHOPT or WBINVD to flush. Since
CLFLUSHOPT is global on x86 and WBINVD is called on each cpu in
drm_clflush_virt_range(), the flush operation is global.
2. Any context switch caused by preemption or page faults (page fault
may cause sleep) doesn't affect the validity of local mapping.
Therefore, cpu_set() and cpu_get() are functions where the use of
kmap_local_page() in place of kmap_atomic() is correctly suited.
Convert the calls of kmap_atomic() / kunmap_atomic() to
kmap_local_page() / kunmap_local().
[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231203132947.2328805-6-zhao1.liu@linux.intel.com
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