Re: Performance drop on XDrawRectangles()

Chris Wilson
2014-01-08T17:10:52Z

On Wed, Jan 08, 2014 at 04:57:52PM +0100, Thomas Richter wrote:
> Hi folks,
>
> during the changes from 3.12rc7 to 3.13rc4, the performance of
> XDrawRectangles() dropped considerably. Interestingly, it is not the
> raw rectangles drawing operations that are slow, but it seems that
> the "per-call" overhead has increased by one magnitude. In specific,
> if you use the unmodified "x11pref" program:
>
> x11pref -rect10
>
> no substiantial changes are visible. However, if the rectangles are
> drawn one by one by changing:
>
> /* snip: old version, lines 86ff of do_rects.c of the x11perf program */
>
> void
> DoRectangles(XParms xp, Parms p, int reps)
> {
> int i;
>
> for (i = 0; i != reps; i++) {
> XFillRectangles(xp->d, xp->w, pgc, rects, p->objects);
> if (pgc == xp->bggc)
> pgc = xp->fggc;
> else
> pgc = xp->bggc;
> CheckAbort ();
> }
> }
>
> /* to the following : */
>
> void
> DoRectangles(XParms xp, Parms p, int reps)
> {
> int i;
> int j;
>
> for (i = 0; i != reps; i++) {
> for(j = 0;j < p->objects;j++) {
> XFillRectangles(xp->d, xp->w, pgc, rects+j, 1);
> }
> if (pgc == xp->bggc)
> pgc = xp->fggc;
> else
> pgc = xp->bggc;
> CheckAbort ();
> }
> }
>
> by instead drawing the rectangles one by one, the performance is
> decreased to one eigths of the original performance:
>
> 400000 trep @ 0.0687 msec ( 14600.0/sec): 10x10 rectangle (new)
> 2500000 trep @ 0.0107 msec ( 93900.0/sec): 10x10 rectangle (old)

Just to be clear: new = 3.13-rc4, old = 3.12-rc7 ?

I've taken a quick look at this on an ivb i7-3270qm, and see a 296kops/s
to 248kops/s decrease. Not massive, and considering the difference in
our hardware probably a distinct issue.