[PATCH] drm/bochs: use ioremap_wc() to map framebuffer during driver probing
Thomas Zimmermann
tzimmermann at suse.de
Mon Sep 9 06:40:30 UTC 2024
Hi
Am 09.09.24 um 07:15 schrieb Yan Zhao:
> Use ioremap_wc() instead of ioremap() to map framebuffer during driver
> probing phase.
>
> Using ioremap() results in a VA being mapped with PAT=UC-. Additionally,
> on x86 architectures, ioremap() invokes memtype_reserve() to reserve the
> memory type as UC- for the physical range. This reservation can cause
> subsequent calls to ioremap_wc() to fail to map the VA with PAT=WC to the
> same physical range for framebuffre in ttm_kmap_iter_linear_io_init().
> Consequently, the operation drm_gem_vram_bo_driver_move() ->
> ttm_bo_move_memcpy() -> ttm_move_memcpy() becomes significantly slow on
> platforms where UC memory access is slow.
I've noticed this too and pushed a major update that replaces the entire
memory management. [1]
The patch is still welcome, I think, but you may want to rebase onto the
latest drm-misc-next branch. [2]
Best regards
Thomas
[1] https://patchwork.freedesktop.org/series/138086/
[2] https://gitlab.freedesktop.org/drm/misc/kernel/-/tree/drm-misc-next
>
> Here's the performance data measured in a guest on the physical machine
> "Sapphire Rapids XCC".
> With host KVM honors guest PAT memory types, the effective memory type
> for this framebuffer range is
> - WC when ioremap_wc() is used in driver probing phase
> - UC- when ioremap() is used.
>
> The data presented is an average from 10 execution runs.
> The memcpy range for the data is
> mem->bus.offset=0xfd000000, mem->size=0x3e8000.
>
> --------------------------------------------------------------
> | in bochs_hw_init() |
> | ioremap() | ioremap_wc() |
> ------------------------------|----------------|--------------|
> cycles of | 2227.4M | 17.8M |
> drm_gem_vram_bo_driver_move() | | |
> ------------------------------|----------------|--------------|
> time of | 1.24s | 0.01s |
> drm_gem_vram_bo_driver_move() | | |
> --------------------------------------------------------------
>
> Reported-by: Vitaly Kuznetsov <vkuznets at redhat.com>
> Closes: https://lore.kernel.org/all/87jzfutmfc.fsf@redhat.com/#t
> Cc: Sean Christopherson <seanjc at google.com>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Kevin Tian <kevin.tian at intel.com>
> Signed-off-by: Yan Zhao <yan.y.zhao at intel.com>
> ---
> drivers/gpu/drm/tiny/bochs.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/tiny/bochs.c b/drivers/gpu/drm/tiny/bochs.c
> index 31fc5d839e10..6414f0a72f6a 100644
> --- a/drivers/gpu/drm/tiny/bochs.c
> +++ b/drivers/gpu/drm/tiny/bochs.c
> @@ -261,7 +261,7 @@ static int bochs_hw_init(struct drm_device *dev)
> if (pci_request_region(pdev, 0, "bochs-drm") != 0)
> DRM_WARN("Cannot request framebuffer, boot fb still active?\n");
>
> - bochs->fb_map = ioremap(addr, size);
> + bochs->fb_map = ioremap_wc(addr, size);
> if (bochs->fb_map == NULL) {
> DRM_ERROR("Cannot map framebuffer\n");
> return -ENOMEM;
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
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