| Message ID | 20220217103405.26492-2-tzimmermann@suse.de |
|---|---|
| State | Superseded |
| Headers | show |
| Series | fbdev: Improve performance of fbdev console | expand |
Hi Thomas, On Thu, Feb 17, 2022 at 11:34:04AM +0100, Thomas Zimmermann wrote: > Improve the performance of sys_fillrect() by using word-aligned > 32/64-bit mov instructions. While the code tried to implement this, > the compiler failed to create fast instructions. The resulting > binary instructions were even slower than cfb_fillrect(), which > uses the same algorithm, but operates on I/O memory. > > A microbenchmark measures the average number of CPU cycles > for sys_fillrect() after a stabilizing period of a few minutes > (i7-4790, FullHD, simpledrm, kernel with debugging). The value > for CFB is given as a reference. > > sys_fillrect(), new: 26586 cycles > sys_fillrect(), old: 166603 cycles > cfb_fillrect(): 41012 cycles > > In the optimized case, sys_fillrect() is now ~6x faster than before > and ~1.5x faster than the CFB implementation. > > Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Nice optimization. Reviewed-by: Sam Ravnborg <sam@ravnborg.org> > --- > drivers/video/fbdev/core/sysfillrect.c | 16 +++------------- > 1 file changed, 3 insertions(+), 13 deletions(-) > > diff --git a/drivers/video/fbdev/core/sysfillrect.c b/drivers/video/fbdev/core/sysfillrect.c > index 33ee3d34f9d2..bcdcaeae6538 100644 > --- a/drivers/video/fbdev/core/sysfillrect.c > +++ b/drivers/video/fbdev/core/sysfillrect.c > @@ -50,19 +50,9 @@ bitfill_aligned(struct fb_info *p, unsigned long *dst, int dst_idx, > > /* Main chunk */ > n /= bits; > - while (n >= 8) { > - *dst++ = pat; > - *dst++ = pat; > - *dst++ = pat; > - *dst++ = pat; > - *dst++ = pat; > - *dst++ = pat; > - *dst++ = pat; > - *dst++ = pat; > - n -= 8; > - } > - while (n--) > - *dst++ = pat; > + memset_l(dst, pat, n); > + dst += n; > + > /* Trailing bits */ > if (last) > *dst = comp(pat, *dst, last); > -- > 2.34.1
diff --git a/drivers/video/fbdev/core/sysfillrect.c b/drivers/video/fbdev/core/sysfillrect.c index 33ee3d34f9d2..bcdcaeae6538 100644 --- a/drivers/video/fbdev/core/sysfillrect.c +++ b/drivers/video/fbdev/core/sysfillrect.c @@ -50,19 +50,9 @@ bitfill_aligned(struct fb_info *p, unsigned long *dst, int dst_idx, /* Main chunk */ n /= bits; - while (n >= 8) { - *dst++ = pat; - *dst++ = pat; - *dst++ = pat; - *dst++ = pat; - *dst++ = pat; - *dst++ = pat; - *dst++ = pat; - *dst++ = pat; - n -= 8; - } - while (n--) - *dst++ = pat; + memset_l(dst, pat, n); + dst += n; + /* Trailing bits */ if (last) *dst = comp(pat, *dst, last);
Improve the performance of sys_fillrect() by using word-aligned 32/64-bit mov instructions. While the code tried to implement this, the compiler failed to create fast instructions. The resulting binary instructions were even slower than cfb_fillrect(), which uses the same algorithm, but operates on I/O memory. A microbenchmark measures the average number of CPU cycles for sys_fillrect() after a stabilizing period of a few minutes (i7-4790, FullHD, simpledrm, kernel with debugging). The value for CFB is given as a reference. sys_fillrect(), new: 26586 cycles sys_fillrect(), old: 166603 cycles cfb_fillrect(): 41012 cycles In the optimized case, sys_fillrect() is now ~6x faster than before and ~1.5x faster than the CFB implementation. Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> --- drivers/video/fbdev/core/sysfillrect.c | 16 +++------------- 1 file changed, 3 insertions(+), 13 deletions(-)