On Sat, Oct 29, 2022 at 03:32:08PM +0200, Fabio M. De Francesco wrote: > Date: Sat, 29 Oct 2022 15:32:08 +0200 > From: "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx> > Subject: Re: [PATCH 2/9] drm/i915: Use kmap_local_page() in > gem/i915_gem_pyhs.c > > On luned? 17 ottobre 2022 11:37:18 CEST Zhao Liu wrote: > > From: Zhao Liu <zhao1.liu@xxxxxxxxx> > > > > The use of kmap_atomic() is being deprecated in favor of > > kmap_local_page()[1]. > > > > The main difference between atomic and local mappings is that local > > mappings doesn't disable page faults or preemption. > > > > In drm/i915/gem/i915_gem_phys.c, the functions > > i915_gem_object_get_pages_phys() and i915_gem_object_put_pages_phys() > > don't need to disable pagefaults and preemption for mapping because of > > these 2 reasons: > > > > 1. The flush operation is safe for CPU hotplug when preemption is not > > disabled. In drm/i915/gem/i915_gem_object.c, the functions > > i915_gem_object_get_pages_phys() and i915_gem_object_put_pages_phys() > > calls 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 and any issue > > with cpu's being added or removed can be handled safely. > > > > 2. Any context switch caused by preemption or sleep (pagefault may > > cause sleep) doesn't affect the validity of local mapping. > > > > Therefore, i915_gem_object_get_pages_phys() and > > i915_gem_object_put_pages_phys() are two 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(). > > > > I have here the same questions as in 1/9. > > > [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@xxxxxxxxx > > > > Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx> > > 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: > > Dave: Referred to his explanation about cache flush. > > Ira: Referred to his task document, review comments and explanation about > > cache flush. > > Fabio: Referred to his boiler plate commit message. > > --- > > drivers/gpu/drm/i915/gem/i915_gem_phys.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > b/drivers/gpu/drm/i915/gem/i915_gem_phys.c index 0d0e46dae559..d602ba19ecb2 > 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c > > @@ -66,10 +66,10 @@ static int i915_gem_object_get_pages_phys(struct > drm_i915_gem_object > > *obj) if (IS_ERR(page)) > > goto err_st; > > > > - src = kmap_atomic(page); > > + src = kmap_local_page(page); > > memcpy(dst, src, PAGE_SIZE); > > drm_clflush_virt_range(dst, PAGE_SIZE); > > - kunmap_atomic(src); > > + kunmap_local(src); > > Please use memcpy_from_page() instead of open coding mapping + memcpy() + > unmapping. Ok. > > > > > put_page(page); > > dst += PAGE_SIZE; > > @@ -114,10 +114,10 @@ i915_gem_object_put_pages_phys(struct > drm_i915_gem_object *obj, > > if (IS_ERR(page)) > > continue; > > > > - dst = kmap_atomic(page); > > + dst = kmap_local_page(page); > > drm_clflush_virt_range(src, PAGE_SIZE); > > memcpy(dst, src, PAGE_SIZE); > > - kunmap_atomic(dst); > > + kunmap_local(dst); > > For the same reasons said above, memcpy_to_page() should be used here and > avoid open coding of three functions. > > Using those helpers forces you to move drm_clflush_virt_range() out of the > mapping / un-mapping region. I may be wrong, however I'm pretty sure that the > relative positions of each of those call sites is something that cannot be > randomly chosen. I agree. Will use memcpy_to_page(). Thanks, Zhao > > Thanks, > > Fabio > > > > > set_page_dirty(page); > > if (obj->mm.madv == I915_MADV_WILLNEED) > > >
