Zhao Liu wrote: > From: Zhao Liu <zhao1.liu@xxxxxxxxx> > > The use of kmap_atomic() is being deprecated in favor of > kmap_local_page()[1], and this patch converts the calls 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 and preemption disables. > > In i915_gem_execbuffer.c, eb->reloc_cache.vaddr is mapped by > kmap_atomic() in eb_relocate_entry(), and is unmapped by > kunmap_atomic() in reloc_cache_reset(). First off thanks for the series and sticking with this. That said this patch kind of threw me for a loop because tracing the map/unmap calls did not make sense to me. See below. > > And this mapping/unmapping occurs in two places: one is in > eb_relocate_vma(), and another is in eb_relocate_vma_slow(). > > The function eb_relocate_vma() or eb_relocate_vma_slow() doesn't > need to disable pagefaults and preemption during the above mapping/ > unmapping. > > So it can simply use kmap_local_page() / kunmap_local() that can > instead do the mapping / unmapping regardless of the context. > > 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@xxxxxxxxx > > v2: No code change since v1. Added description of the motivation of > using kmap_local_page() and "Suggested-by" tag of Fabio. > > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Suggested-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> > Signed-off-by: Zhao Liu <zhao1.liu@xxxxxxxxx> > --- > Suggested by credits: > Ira: Referred to his task document, review comments. > Fabio: Referred to his boiler plate commit message and his description > about why kmap_local_page() should be preferred. > --- > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > index 9dce2957b4e5..805565edd148 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > @@ -1151,7 +1151,7 @@ static void reloc_cache_unmap(struct reloc_cache *cache) > > vaddr = unmask_page(cache->vaddr); > if (cache->vaddr & KMAP) > - kunmap_atomic(vaddr); > + kunmap_local(vaddr); In the cover letter you don't mention this unmap path. Rather you mention only reloc_cache_reset(). After digging into this and considering these are kmap_atomic() calls I _think_ what you have is ok. But I think I'd like to see the call paths documented a bit more clearly. Or perhaps cleaned up a lot. For example I see the following call possibility from a user ioctl. In this trace I see 2 examples where something is unmapped first. I don't understand why that is required? I would assume reloc_cache_unmap() and reloc_kmap() are helpers called from somewhere else requiring a remapping of the cache but I don't see it. i915_gem_execbuffer2_ioctl() eb_relocate_parse() eb_relocate_parse_slow() eb_relocate_vma_slow() eb_relocate_entry() reloc_cache_unmap() kunmap_atomic() <=== HERE! reloc_cache_remap() kmap_atomic() relocate_entry() reloc_vaddr() reloc_kmap() kunmap_atomic() <== HERE! kmap_atomic() reloc_cache_reset() kunmap_atomic() Could these mappings be cleaned up a lot more? Perhaps by removing some of the helper functions which AFAICT are left over from older versions of the code? Also as an aside I think it is really bad that eb_relocate_entry() returns negative errors in a u64. Better to get the types right IMO. Thanks for the series! Ira > else > io_mapping_unmap_atomic((void __iomem *)vaddr); > } > @@ -1167,7 +1167,7 @@ static void reloc_cache_remap(struct reloc_cache *cache, > if (cache->vaddr & KMAP) { > struct page *page = i915_gem_object_get_page(obj, cache->page); > > - vaddr = kmap_atomic(page); > + vaddr = kmap_local_page(page); > cache->vaddr = unmask_flags(cache->vaddr) | > (unsigned long)vaddr; > } else { > @@ -1197,7 +1197,7 @@ static void reloc_cache_reset(struct reloc_cache *cache, struct i915_execbuffer > if (cache->vaddr & CLFLUSH_AFTER) > mb(); > > - kunmap_atomic(vaddr); > + kunmap_local(vaddr); > i915_gem_object_finish_access(obj); > } else { > struct i915_ggtt *ggtt = cache_to_ggtt(cache); > @@ -1229,7 +1229,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj, > struct page *page; > > if (cache->vaddr) { > - kunmap_atomic(unmask_page(cache->vaddr)); > + kunmap_local(unmask_page(cache->vaddr)); > } else { > unsigned int flushes; > int err; > @@ -1251,7 +1251,7 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj, > if (!obj->mm.dirty) > set_page_dirty(page); > > - vaddr = kmap_atomic(page); > + vaddr = kmap_local_page(page); > cache->vaddr = unmask_flags(cache->vaddr) | (unsigned long)vaddr; > cache->page = pageno; > > -- > 2.34.1 >
