Where olpc machine spending time when using web broswer

[Owen Williams]

This is a total non-expert opinion, but aren't we scaling all of the
images to correct for the high-dpi screen?  That sounds like it would
call for bilinear filtering.

owen


On Tue, 2007-03-13 at 11:52 -0400, Adam Jackson wrote:
> On Mon, 2007-03-12 at 18:59 -0400, William Cohen wrote:
> 
> > # opreport -t 1 -l /usr/bin/Xorg
> > CPU: CPU with timer interrupt, speed 0 MHz (estimated)
> > Profiling through timer interrupt
> > samples  %        image name               symbol name
> > 6514     68.1096  libfb.so                 fbFetchTransformed
> 
> Wow.  I think that's the first time I've ever seen this actually show up
> on a profile.  I didn't think anything used Render's transformations on
> account of they're so painfully slow.
> 
> > 613       6.4095  libfb.so                 fbFetchPixel_x8r8g8b8
> 
> Just as an aside, gcc generates some intensely dumb code:
> 
> 00000d80 <fbFetchPixel_x8r8g8b8>:
>      d80:       55                      push   %ebp
>      d81:       8b 04 90                mov    (%eax,%edx,4),%eax
>      d84:       89 e5                   mov    %esp,%ebp
>      d86:       5d                      pop    %ebp
>      d87:       0d 00 00 00 ff          or     $0xff000000,%eax
>      d8c:       c3                      ret    
>      d8d:       8d 76 00                lea    0x0(%esi),%esi
> 
> Yay for frame pointers on leaf functions!  I guess we can build X with
> -momit-leaf-frame-pointer, it can't hurt but I have no idea if it'll
> help measurably.  It certainly makes the code prettier:
> 
> 00000ce0 <fbFetchPixel_x8r8g8b8>:
>      ce0:       8b 04 90                mov    (%eax,%edx,4),%eax
>      ce3:       0d 00 00 00 ff          or     $0xff000000,%eax
>      ce8:       c3                      ret    
>      ce9:       8d b4 26 00 00 00 00    lea    0x0(%esi),%esi
> 
> >    398  6.1099 :                        x1 = MOD (x1, pict->pDrawable->width);
> >    383  5.8796 :                        x2 = MOD (x2, pict->pDrawable->width);
> >    336  5.1581 :                        y1 = MOD (y1, pict->pDrawable->height);
> >    355  5.4498 :                        y2 = MOD (y2, pict->pDrawable->height);
> 
> It feels like we ought to be able to MMX this pattern.
> 
> >                :                        ft = FbGet8(tl,0) * idistx + FbGet8(tr,0) * distx;
> >                :                        fb = FbGet8(bl,0) * idistx + FbGet8(br,0) * distx;
> >    536  8.2284 :                        r = (((ft * idisty + fb * disty) >> 16) & 0xff);
> >                :                        ft = FbGet8(tl,8) * idistx + FbGet8(tr,8) * distx;
> >                :                        fb = FbGet8(bl,8) * idistx + FbGet8(br,8) * distx;
> >    482  7.3994 :                        r |= (((ft * idisty + fb * disty) >> 8) & 0xff00);
> >                :                        ft = FbGet8(tl,16) * idistx + FbGet8(tr,16) * distx;
> >                :                        fb = FbGet8(bl,16) * idistx + FbGet8(br,16) * distx;
> >    514  7.8907 :                        r |= (((ft * idisty + fb * disty)) & 0xff0000);
> >                :                        ft = FbGet8(tl,24) * idistx + FbGet8(tr,24) * distx;
> >                :                        fb = FbGet8(bl,24) * idistx + FbGet8(br,24) * distx;
> >                :                        r |= (((ft * idisty + fb * disty) << 8) & 0xff000000);
> >    512  7.8600 :                        buffer[i] = r;
> 
> And maybe this one.
> 
> But the more serious question is why we're hitting this path at all.  I
> can't think of anything in the described firefox use profile that would
> require filters or transformations.  The only place I can see the word
> 'bilinear' mentioned at all in firefox is
> 
> modules/libpr0n/decoders/icon/gtk/nsIconChannel.cpp:
>     nsIconChannel::InitWithGnome()
> 
> but that seems unlikely.  And more importantly it doesn't look like
> we'll ever hit fbFetchTransformed without an actual transformation
> matrix.  Someone who knows firefox want to chime in here?
> 
> - ajax
> 
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