On Wed, 10 Oct 2012 11:21:44 +0200, Daniel Vetter <daniel at ffwll.ch> wrote: > On Wed, Oct 10, 2012 at 10:01:47AM +0100, Chris Wilson wrote: > > On Tue, 09 Oct 2012 23:16:02 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote: > > > On Tue, 9 Oct 2012 22:50:48 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > > > > The obj->pages to obj->pages->sgl rework introduced this helper, but > > > > it doesn't actually work for n >= SG_MAX_SINGLE_ALLOC. > > > > > > > > For simplicity (and since right now I seem to be too stupid to see > > > > the bug), let's just grab the right page with a for_each_sg loop. > > > > > > > > This is exercised by the improved hangman tests and the gem_exec_big > > > > test in i-g-t. > > > > > > > > v2: Compared to v1, don't try to be clever since I seemingly only > > > > manage to prove that I'm not clever. > > > > > > Only I expect that loop to show up on profiles even higher than the > > > sg_next() from pwrite. :| > > > > > > I expect it to have a measureable impact upon relocation throughput, > > > so I should measure it... > > > -Chris > > > > > > -- > > > Chris Wilson, Intel Open Source Technology Centre > > > _______________________________________________ > > > Intel-gfx mailing list > > > Intel-gfx at lists.freedesktop.org > > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > > From: Chris Wilson <chris at chris-wilson.co.uk> > > Subject: Re: [PATCH] drm/i915: fixup i915_gem_object_get_page inline helper > > To: Daniel Vetter <daniel.vetter at ffwll.ch>, Intel Graphics Development <intel-gfx at lists.freedesktop.org> > > Cc: Daniel Vetter <daniel.vetter at ffwll.ch> > > In-Reply-To: <1349815848-1824-1-git-send-email-daniel.vetter at ffwll.ch> > > References: <84c8a8$624sk4 at orsmga001.jf.intel.com> <1349815848-1824-1-git-send-email-daniel.vetter at ffwll.ch> > > > > On Tue, 9 Oct 2012 22:50:48 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > > > The obj->pages to obj->pages->sgl rework introduced this helper, but > > > it doesn't actually work for n >= SG_MAX_SINGLE_ALLOC. > > > > > > For simplicity (and since right now I seem to be too stupid to see > > > the bug), let's just grab the right page with a for_each_sg loop. > > > > > > This is exercised by the improved hangman tests and the gem_exec_big > > > test in i-g-t. > > > > > > v2: Compared to v1, don't try to be clever since I seemingly only > > > manage to prove that I'm not clever. > > > > > > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> > > > > Looks like my worries are baseless. It can always be attacked latter if > > need be. I'd still like to know what the mistake was... > > > > Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> > > Merged to -fixes, with the missing regression-sha1 citation added. > -Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch From: Chris Wilson <chris at chris-wilson.co.uk> Subject: Re: [PATCH] drm/i915: fixup i915_gem_object_get_page inline helper To: Daniel Vetter <daniel at ffwll.ch> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>, Intel Graphics Development <intel-gfx at lists.freedesktop.org> In-Reply-To: <20121010091538.GB5533 at phenom.ffwll.local> References: <84c8a8$624sk4 at orsmga001.jf.intel.com> <1349815848-1824-1-git-send-email-daniel.vetter at ffwll.ch> <6c3329$6m595h at orsmga002.jf.intel.com> <453bf0$61a4mf at azsmga001.ch.intel.com> <20121010091538.GB5533 at phenom.ffwll.local> On Wed, 10 Oct 2012 11:15:38 +0200, Daniel Vetter <daniel at ffwll.ch> wrote: > On Wed, Oct 10, 2012 at 10:01:47AM +0100, Chris Wilson wrote: > > On Tue, 09 Oct 2012 23:16:02 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote: > > > On Tue, 9 Oct 2012 22:50:48 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > > > > The obj->pages to obj->pages->sgl rework introduced this helper, but > > > > it doesn't actually work for n >= SG_MAX_SINGLE_ALLOC. > > > > > > > > For simplicity (and since right now I seem to be too stupid to see > > > > the bug), let's just grab the right page with a for_each_sg loop. > > > > > > > > This is exercised by the improved hangman tests and the gem_exec_big > > > > test in i-g-t. > > > > > > > > v2: Compared to v1, don't try to be clever since I seemingly only > > > > manage to prove that I'm not clever. > > > > > > Only I expect that loop to show up on profiles even higher than the > > > sg_next() from pwrite. :| > > > > > > I expect it to have a measureable impact upon relocation throughput, > > > so I should measure it... > > > -Chris > > > > > > -- > > > Chris Wilson, Intel Open Source Technology Centre > > > _______________________________________________ > > > Intel-gfx mailing list > > > Intel-gfx at lists.freedesktop.org > > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > > From: Chris Wilson <chris at chris-wilson.co.uk> > > Subject: Re: [PATCH] drm/i915: fixup i915_gem_object_get_page inline helper > > To: Daniel Vetter <daniel.vetter at ffwll.ch>, Intel Graphics Development <intel-gfx at lists.freedesktop.org> > > Cc: Daniel Vetter <daniel.vetter at ffwll.ch> > > In-Reply-To: <1349815848-1824-1-git-send-email-daniel.vetter at ffwll.ch> > > References: <84c8a8$624sk4 at orsmga001.jf.intel.com> <1349815848-1824-1-git-send-email-daniel.vetter at ffwll.ch> > > > > On Tue, 9 Oct 2012 22:50:48 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > > > The obj->pages to obj->pages->sgl rework introduced this helper, but > > > it doesn't actually work for n >= SG_MAX_SINGLE_ALLOC. > > > > > > For simplicity (and since right now I seem to be too stupid to see > > > the bug), let's just grab the right page with a for_each_sg loop. > > > > > > This is exercised by the improved hangman tests and the gem_exec_big > > > test in i-g-t. > > > > > > v2: Compared to v1, don't try to be clever since I seemingly only > > > manage to prove that I'm not clever. > > > > > > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> > > > > Looks like my worries are baseless. It can always be attacked latter if > > need be. I'd still like to know what the mistake was... > > I think it was two mistakes: > - One was the off-by-one fixed in v1. > - Second seemed to be the special case that if the table fits exactly, > sg_alloc doesn't set a chain ptr with another sg table with just one > entry. That oddity is the reason why the loop was structured so. The mistake is that just because we have n == MAX, does not mean that there are only n elements left in the sg! *hides* diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index d2dda78..e6707e7 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -1383,9 +1383,14 @@ int __must_check i915_gem_object_get_pages(struct drm_i91 static inline struct page *i915_gem_object_get_page(struct drm_i915_gem_object { struct scatterlist *sg = obj->pages->sgl; - while (n >= SG_MAX_SINGLE_ALLOC) { + int nents = obj->pages->orig; + while (nents > SG_MAX_SINGLE_ALLOC) { + if (n < SG_MAX_SINGLE_ALLOC - 1) + break; + sg = sg_chain_ptr(sg + SG_MAX_SINGLE_ALLOC - 1); n -= SG_MAX_SINGLE_ALLOC - 1; + nents -= SG_MAX_SINGLE_ALLOC - 1; } return sg_page(sg+n); } -Chris -- Chris Wilson, Intel Open Source Technology Centre
