It just influence one page. During my test, I found one read slow path info when enable prefault. So I add this patch. Why don't move fault_in_multipages_writeable() from i915_gem_shmem_pread() to the beginning of i915_gem_pread_ioctl() ? So the pread_ioctl() is like pwrite_ioctl(). Is the cost of fault_in_multipages_writeable() lager than fault_in_multipages_readable() ? See the attachment.
thanks -----Original Message----- From: Daniel Vetter [mailto:daniel.vet...@ffwll.ch] On Behalf Of Daniel Vetter Sent: Friday, July 19, 2013 3:29 PM To: Zhang, Xiong Y Cc: intel-gfx@lists.freedesktop.org; Chris Wilson Subject: Re: [Intel-gfx] [PATCH 3/3] drm/i915: run shmem_pread_fast() after page fault On Fri, Jul 19, 2013 at 01:51:26PM +0800, Xiong Zhang wrote: > fault_in_multipages_writeable() will load fault page into physical > memory, then pread can run fast path, no need to run slow path > > Signed-off-by: Xiong Zhang <xiong.y.zh...@intel.com> Hm, this avoids going through the slowpath for the first page. Does this have an impact on micro-benchmarks (we have a few) or is this just something you've spotted? I'm a bit vary of making the already complicated shmem pread/pwrite paths even more complicated. Chris? -Daniel > --- > drivers/gpu/drm/i915/i915_gem.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c > b/drivers/gpu/drm/i915/i915_gem.c index f194d7e..982df1e 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -459,6 +459,7 @@ i915_gem_shmem_pread(struct drm_device *dev, > page_do_bit17_swizzling = obj_do_bit17_swizzling && > (page_to_phys(page) & (1 << 17)) != 0; > > +read_again: > ret = shmem_pread_fast(page, shmem_page_offset, page_length, > user_data, page_do_bit17_swizzling, > needs_clflush); > @@ -475,6 +476,8 @@ i915_gem_shmem_pread(struct drm_device *dev, > * and just continue. */ > (void)ret; > prefaulted = 1; > + mutex_lock(&dev->struct_mutex); > + goto read_again; > } > > ret = shmem_pread_slow(page, shmem_page_offset, page_length, > -- > 1.8.3.2 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
0001-drm-i915-move-page-fault-handle-to-i915_gem_pread_io.patch
Description: 0001-drm-i915-move-page-fault-handle-to-i915_gem_pread_io.patch
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