On 28.08.23 23:54, Heinrich Schuchardt wrote:
On 8/28/23 22:24, Alexander Graf wrote:On 28.08.23 19:54, Simon Glass wrote:Hi Alex, On Wed, 23 Aug 2023 at 02:56, Alexander Graf <ag...@csgraf.de> wrote:Hey Simon, On 22.08.23 20:56, Simon Glass wrote:Hi Alex, On Tue, 22 Aug 2023 at 01:47, Alexander Graf <ag...@csgraf.de> wrote:On 22.08.23 01:03, Simon Glass wrote:I can't think of any heuristic that would reliably work. Relevant forHi Alex,On Mon, 21 Aug 2023 at 16:40, Alexander Graf <ag...@csgraf.de> wrote:On 22.08.23 00:10, Simon Glass wrote:Hi Alex, On Mon, 21 Aug 2023 at 14:20, Alexander Graf <ag...@csgraf.de> wrote:On 21.08.23 21:57, Simon Glass wrote:Hi Alex, On Mon, 21 Aug 2023 at 13:33, Alexander Graf <ag...@csgraf.de> wrote:On 21.08.23 21:11, Simon Glass wrote:Hi Alper, On Mon, 21 Aug 2023 at 07:51, Alper Nebi Yasak <alpernebiya...@gmail.com> wrote:This is a rebase of Alexander Graf's video damage tracking series, with some tests and other changes. The original cover letter is as follows:This patch set speeds up graphics output on ARM by a factor of 60x. On most ARM SBCs, we keep the frame buffer in DRAM and map it as cached, but need it accessible by the display controller which reads directly from a later point of consistency. Hence, we flush the frame buffer to DRAM on every change. The full frame buffer.It should not, see below.Unfortunately, with the advent of 4k displays, we are seeing frame buffers that can take a while to flush out. This was reported by Da Xue with grub, which happily print 1000s of spaces on the screen to draw a menu. Every printed space triggers a cache flush.That is a bug somewhere in EFI.Unfortunately not :). You may call it a bug in grub: It literally prints over space characters for every character in its menu that it wants cleared. On every text screen draw. This wouldn't be a big issue if we only flush the reactangle that gets modified. But without this patch set, we're flushing the full DRAM buffer on every u-boot text console character write, which means for every character (as that's the only API UEFI has). As a nice side effect, we speed up the normal U-Boot text console as well with this patch set, because even "normal" text prints that write for example a single line of text on the screen today flush the full frame buffer to DRAM.No, I mean that it is a bug that U-Boot (apparently) flushes the cache after every character. It doesn't do that for normal character output and I don't think it makes sense to do it for EFI either.I see. Let's trace the calls: efi_cout_output_string() -> fputs() -> vidconsole_puts() -> video_sync() -> flush_dcache_range()Unfortunately grub abstracts character backends down to the "print character" level, so it calls UEFI's sopisticated "output_string"callback with single characters at a time, which means we do a full dcache flush for every character that we print:https://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/term/efi/console.c#n165This patch set implements the easiest mitigation against this problem: Damage tracking. We remember the lowest common denominator region that was touched since the last video_sync() call and only flush that. The most typical writer to the frame buffer is the video console, which always writes rectangles of characters on the screen and syncs afterwards. With this patch set applied, we reduce drawing a large grub menu (with serial console attached for size information) on an RK3399-ROC system at 1440p from 55 seconds to less than 1 second. Version 2 also implements VIDEO_COPY using this mechanism, reducing its overhead compared to before as well. So even x86 systems should be faster with this now :). Alternatives considered: 1) Lazy sync - Sandbox does this. It only calls video_sync(true) ever so often. We are missing timers to do this generically. 2) Double buffering - We could try to identify whether anything changed at all and only draw to the FB if it did. That would requiremaintaining a second buffer that we need to scan.3) Text buffer - Maintain a buffer of all text printed on the screen with respective location. Don't write if the old and new character are identical. This would limit applicability to text only and is an optimization on top of this patch set. 4) Hash screen lines - Create a hash (sha256?) over every line when it changes. Only flush when it does. I'm not sure if this would waste more time, memory and cache than the current approach. It would make full screen updates much more expensive.5) Fix the bug mentioned above?Changes in v5: - Add patch "video: test: Split copy frame buffer check into a function" - Add patch "video: test: Support checking copy frame buffer contents" - Add patch "video: test: Test partial updates of hardware frame buffer" - Use xstart, ystart, xend, yend as names for damage region - Document damage struct and fields in struct video_priv comment - Return void from video_damage() - Fix undeclared priv error in video_sync() - Drop unused headers from video-uclass.c - Use IS_ENABLED() instead of CONFIG_IS_ENABLED() - Call video_damage() also in video_fill_part() - Use met->baseline instead of priv->baseline - Use fontdata->height/width instead of VIDEO_FONT_HEIGHT/WIDTH - Update console_rotate.c video_damage() calls to pass video tests - Remove mention about not having minimal damage for console_rotate.c - Add patch "video: test: Test video damage tracking via vidconsole" - Document new vdev field in struct efi_gop_obj comment - Remove video_sync_copy() also from video_fill(), video_fill_part() - Fix memmove() calls by removing the extra dev argument - Call video_sync() before checking copy_fb in video tests- Imply VIDEO_DAMAGE for video drivers instead of selecting it- Imply VIDEO_DAMAGE also for VIDEO_TIDSS v4:https://lore.kernel.org/all/20230103215004.22646-1-ag...@csgraf.de/Changes in v4: - Move damage clear to patch "dm: video: Add damage tracking API" - Simplify first damage logic - Remove VIDEO_DAMAGE default for ARM - Skip damage on EfiBltVideoToBltBuffer - Add patch "video: Always compile cache flushing code" - Add patch "video: Enable VIDEO_DAMAGE for drivers that need it" v3:https://lore.kernel.org/all/20221230195828.88134-1-ag...@csgraf.de/Changes in v3: - Adapt to always assume DM is used - Adapt to always assume DM is used - Make VIDEO_COPY always select VIDEO_DAMAGE v2:https://lore.kernel.org/all/20220609225921.62462-1-ag...@csgraf.de/Changes in v2: - Remove ifdefs - Fix ranges in truetype target - Limit rotate to necessary damage - Remove ifdefs from gop - Fix dcache range; we were flushing too much before - Add patch "video: Use VIDEO_DAMAGE for VIDEO_COPY" v1:https://lore.kernel.org/all/20220606234336.5021-1-ag...@csgraf.de/Alexander Graf (9): dm: video: Add damage tracking API dm: video: Add damage notification on display fills vidconsole: Add damage notifications to all vidconsole drivers video: Add damage notification on bmp display efi_loader: GOP: Add damage notification on BLT video: Only dcache flush damaged lines video: Use VIDEO_DAMAGE for VIDEO_COPY video: Always compile cache flushing code video: Enable VIDEO_DAMAGE for drivers that need it Alper Nebi Yasak (4): video: test: Split copy frame buffer check into a function video: test: Support checking copy frame buffer contents video: test: Test partial updates of hardware frame buffervideo: test: Test video damage tracking via vidconsolearch/arm/mach-omap2/omap3/Kconfig | 1 + arch/arm/mach-sunxi/Kconfig | 1 + drivers/video/Kconfig | 26 +++ drivers/video/console_normal.c | 27 ++-- drivers/video/console_rotate.c | 94 +++++++---- drivers/video/console_truetype.c | 37 +++-- drivers/video/exynos/Kconfig | 1 + drivers/video/imx/Kconfig | 1 + drivers/video/meson/Kconfig | 1 + drivers/video/rockchip/Kconfig | 1 + drivers/video/stm32/Kconfig | 1 + drivers/video/tegra20/Kconfig | 1 + drivers/video/tidss/Kconfig | 1 + drivers/video/vidconsole-uclass.c | 16 -- drivers/video/video-uclass.c | 190 ++++++++++++---------- drivers/video/video_bmp.c | 7 +- include/video.h | 59 +++---- include/video_console.h | 52 ------ lib/efi_loader/efi_gop.c | 7 + test/dm/video.c | 256 ++++++++++++++++++++++++------ 20 files changed, 483 insertions(+), 297 deletions(-)It is good to see this tidied up into something that can be applied! I am unsure what is going on with the EFI performance, though. It should not flush the cache after every character, only after a new line. Is there something wrong in here? If so, we should fix that bug first and it should be patch 1 of this series.Before I came up with this series, I was trying to identify the UEFI bug in question as well, because intuition told me surely this is a bug in UEFI :). Turns out it really isn't this time around.I don't mean a bug in UEFI, I mean a bug in U-Boot's EFI implementation. Where did you look for the bug?The "real" bug is in grub. But given that it's reasonably simple to work around in U-Boot and even with it "fixed" in grub we would still see performance benefits from flushing only parts of the screen, I think it's worth living with the grub deficiency.OK thanks for digging into it. I suggest we add a param to vidconsole_puts() to tell it whether to sync or not, then the EFI code can indicate this and try to be a bit smarter about it.It doesn't know when to sync either. From its point of view, any"console output" could be the last one. There is no API in UEFI thatsays "please flush console output now".Yes, I understand. I was not suggesting we were missing an API. Butsome sort of heuristic would do, e.g. only flush on a newline, flushevery 50 chars, etc.this conversation, UEFI provides 2 calls: * Write string to screen (efi_cout_output_string)* Set text cursor position to X, Y (efi_cout_set_cursor_position)It's perfectly legal for a UEFI application to do something like efi_cout_set_cursor_position(10, 10); efi_cout_output_string("f"); efi_cout_output_string("o"); efi_cout_output_string("o") ;to update contents of a virtual text box on the screen. Where in thischain of events would we call video_sync(), but on every call to efi_cout_output_string()?Actually U-Boot has the same problem, but we have managed to work out something.U-Boot as a code base has a much easier stance: It can add APIs when it needs them in places that require them. With UEFI (as well as the U-Bootnative API), we're stuck with what's there. I also don't understand what you mean by "we have managed to work out something". This patch set is not a UEFI fix - it fixes generic U-Bootbehavior and speeds up non-UEFI boots as well. The improvement there isjust not as impressive as with grub :).We are still not quite on the same page... U-Boot does have video_sync() but it doesn't know when to call it. If it does not call it, then any amount of single-threaded code can run after that, which may update the framebuffer. In other words, U-Boot is in exactly the same boat as UEFI. It has to decide whether to call video_sync() based on some sort of heuristic. That is the only point I am trying to make here. Does that make sense?Oh, I thought you mentioned above that U-Boot is in a better spot or "has it solved already". I agree - it's in the same boat and the only safe thing it can really do today that is fully cross-platform compatible is to call video_sync() after every character. I don't understand what you mean by "any amount of single-threaded code can run after that, which may update the framebuffer". Any framebuffer modification is U-Boot internal code which then again can apply video_sync() to tell the system "I want what I wrote to screen actually be on screen now". I don't think that's necessarily bad design. A bit clunky, but we're in a pre-boot environment after all. Since we're aligned now: What exactly did you refer to with "but we have managed to work out something"?Should we set PixelBltOnly to indicate to UEFI applications that they are not allowed to directly write to the framebuffer but always have to use BitBlt? GRUB seems to be using a shadow buffer by default which it copies via BitBlt.
If we do that, OSs will no longer be able to carry the frame buffer address over and continue to use it with to draw on the screen natively (like Linux's efifb).
So no, I don't think we should indicate PixelBltOnly. The frame buffer is usually available to applications, you just need to adhere to the architecture's caching constraints.
Alex
