On Thu, Feb 10, 2022 at 03:11:13PM +0100, Thomas Zimmermann wrote: > Fbdev's deferred I/O sorts all dirty pages by default, which incurs a > significant overhead. Make the sorting step optional and update the few > drivers that require it. Use a FIFO list by default. > > Sorting pages by memory offset for deferred I/O performs an implicit > bubble-sort step on the list of dirty pages. The algorithm goes through > the list of dirty pages and inserts each new page according to its > index field. Even worse, list traversal always starts at the first > entry. As video memory is most likely updated scanline by scanline, the > algorithm traverses through the complete list for each updated page. > > For example, with 1024x768x32bpp a page covers exactly one scanline. > Writing a single screen update from top to bottom requires updating > 768 pages. With an average list length of 384 entries, a screen update > creates (768 * 384 =) 294912 compare operation. > > Fix this by making the sorting step opt-in and update the few drivers > that require it. All other drivers work with unsorted page lists. Pages > are appended to the list. Therefore, in the common case of writing the > framebuffer top to bottom, pages are still sorted by offset, which may > have a positive effect on performance. > > Playing a video [1] in mplayer's benchmark mode shows the difference > (i7-4790, FullHD, simpledrm, kernel with debugging). > > mplayer -benchmark -nosound -vo fbdev ./big_buck_bunny_720p_stereo.ogg > > With sorted page lists: > > BENCHMARKs: VC: 32.960s VO: 73.068s A: 0.000s Sys: 2.413s = 108.441s > BENCHMARK%: VC: 30.3947% VO: 67.3802% A: 0.0000% Sys: 2.2251% = 100.0000% > > With unsorted page lists: > > BENCHMARKs: VC: 31.005s VO: 42.889s A: 0.000s Sys: 2.256s = 76.150s > BENCHMARK%: VC: 40.7156% VO: 56.3219% A: 0.0000% Sys: 2.9625% = 100.0000% > > VC shows the overhead of video decoding, VO shows the overhead of the > video output. Using unsorted page lists reduces the benchmark's run time > by ~32s/~25%. Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> from fbtft perspective, thanks! > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx> > Link: https://download.blender.org/peach/bigbuckbunny_movies/big_buck_bunny_720p_stereo.ogg # [1] > --- > drivers/staging/fbtft/fbtft-core.c | 1 + > drivers/video/fbdev/broadsheetfb.c | 1 + > drivers/video/fbdev/core/fb_defio.c | 19 ++++++++++++------- > drivers/video/fbdev/metronomefb.c | 1 + > drivers/video/fbdev/udlfb.c | 1 + > include/linux/fb.h | 1 + > 6 files changed, 17 insertions(+), 7 deletions(-) > > diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c > index f2684d2d6851..4a35347b3020 100644 > --- a/drivers/staging/fbtft/fbtft-core.c > +++ b/drivers/staging/fbtft/fbtft-core.c > @@ -654,6 +654,7 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display, > fbops->fb_blank = fbtft_fb_blank; > > fbdefio->delay = HZ / fps; > + fbdefio->sort_pagelist = true; > fbdefio->deferred_io = fbtft_deferred_io; > fb_deferred_io_init(info); > > diff --git a/drivers/video/fbdev/broadsheetfb.c b/drivers/video/fbdev/broadsheetfb.c > index fd66f4d4a621..b9054f658838 100644 > --- a/drivers/video/fbdev/broadsheetfb.c > +++ b/drivers/video/fbdev/broadsheetfb.c > @@ -1059,6 +1059,7 @@ static const struct fb_ops broadsheetfb_ops = { > > static struct fb_deferred_io broadsheetfb_defio = { > .delay = HZ/4, > + .sort_pagelist = true, > .deferred_io = broadsheetfb_dpy_deferred_io, > }; > > diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c > index 3727b1ca87b1..1f672cf253b2 100644 > --- a/drivers/video/fbdev/core/fb_defio.c > +++ b/drivers/video/fbdev/core/fb_defio.c > @@ -132,15 +132,20 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf) > if (!list_empty(&page->lru)) > goto page_already_added; > > - /* we loop through the pagelist before adding in order > - to keep the pagelist sorted */ > - list_for_each_entry(cur, &fbdefio->pagelist, lru) { > - if (cur->index > page->index) > - break; > + if (fbdefio->sort_pagelist) { > + /* > + * We loop through the pagelist before adding in order > + * to keep the pagelist sorted. > + */ > + list_for_each_entry(cur, &fbdefio->pagelist, lru) { > + if (cur->index > page->index) > + break; > + } > + list_add_tail(&page->lru, &cur->lru); > + } else { > + list_add_tail(&page->lru, &fbdefio->pagelist); > } > > - list_add_tail(&page->lru, &cur->lru); > - > page_already_added: > mutex_unlock(&fbdefio->lock); > > diff --git a/drivers/video/fbdev/metronomefb.c b/drivers/video/fbdev/metronomefb.c > index 952826557a0c..af858dd23ea6 100644 > --- a/drivers/video/fbdev/metronomefb.c > +++ b/drivers/video/fbdev/metronomefb.c > @@ -568,6 +568,7 @@ static const struct fb_ops metronomefb_ops = { > > static struct fb_deferred_io metronomefb_defio = { > .delay = HZ, > + .sort_pagelist = true, > .deferred_io = metronomefb_dpy_deferred_io, > }; > > diff --git a/drivers/video/fbdev/udlfb.c b/drivers/video/fbdev/udlfb.c > index b9cdd02c1000..184bb8433b78 100644 > --- a/drivers/video/fbdev/udlfb.c > +++ b/drivers/video/fbdev/udlfb.c > @@ -980,6 +980,7 @@ static int dlfb_ops_open(struct fb_info *info, int user) > > if (fbdefio) { > fbdefio->delay = DL_DEFIO_WRITE_DELAY; > + fbdefio->sort_pagelist = true; > fbdefio->deferred_io = dlfb_dpy_deferred_io; > } > > diff --git a/include/linux/fb.h b/include/linux/fb.h > index 3d7306c9a706..9a77ab615c36 100644 > --- a/include/linux/fb.h > +++ b/include/linux/fb.h > @@ -204,6 +204,7 @@ struct fb_pixmap { > struct fb_deferred_io { > /* delay between mkwrite and deferred handler */ > unsigned long delay; > + bool sort_pagelist; /* sort pagelist by offset */ > struct mutex lock; /* mutex that protects the page list */ > struct list_head pagelist; /* list of touched pages */ > /* callback */ > -- > 2.34.1 > -- With Best Regards, Andy Shevchenko
