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Message-ID: <75c8c1f0-d774-4bc1-ba71-bce15db921c7@suse.de>
Date: Tue, 10 Sep 2024 09:24:22 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Yan Zhao <yan.y.zhao@...el.com>, kraxel@...hat.com,
maarten.lankhorst@...ux.intel.com, mripard@...nel.org, airlied@...il.com,
daniel@...ll.ch, virtualization@...ts.linux.dev,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc: pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org,
Vitaly Kuznetsov <vkuznets@...hat.com>, Kevin Tian <kevin.tian@...el.com>
Subject: Re: [PATCH v2] drm/bochs: use devm_ioremap_wc() to map framebuffer
Hi
Am 09.09.24 um 15:16 schrieb Yan Zhao:
> Opt for devm_ioremap_wc() over devm_ioremap() when mapping the framebuffer.
>
> Using devm_ioremap() results in the VA being mapped with PAT=UC-, which
> considerably slows down drm_fb_memcpy(). In contrast, devm_ioremap_wc()
> maps the VA with PAT set to WC, leading to better performance on platforms
> where access to UC memory is much slower than WC memory.
>
> 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 devm_ioremap_wc() is used
> - UC- when devm_ioremap() is used.
>
> The data presented is an average from 10 execution runs.
>
> Cycles: Avg cycles of executed bochs_primary_plane_helper_atomic_update()
> from VM boot to GDM show up
> Cnt: Avg cnt of executed bochs_primary_plane_helper_atomic_update()
> from VM boot to GDM show up
> T: Avg time of each bochs_primary_plane_helper_atomic_update().
>
> -------------------------------------------------
> | | devm_ioremap() | devm_ioremap_wc() |
> |------------|----------------|-------------------|
> | Cycles | 211.545M | 0.157M |
> |------------|----------------|-------------------|
> | Cnt | 142 | 1917 |
> |------------|----------------|-------------------|
> | T | 0.1748s | 0.0004s |
> -------------------------------------------------
Very nice. Thank you so much.
> Note:
> Following the rebase to [3], the previously reported GDM failure on the
> VGA device [1] can no longer be reproduced, thanks to the memory management
> improvements made in [2]. Despite this, I have proceeded to submit this
> patch because of the noticeable performance improvements it provides.
>
> Reported-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Closes: https://lore.kernel.org/all/87jzfutmfc.fsf@redhat.com/#t
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> Link: https://lore.kernel.org/all/87jzfutmfc.fsf@redhat.com/#t [1]
> Link: https://patchwork.freedesktop.org/series/138086 [2]
> Link: https://gitlab.freedesktop.org/drm/misc/kernel/-/tree/drm-misc-next [3]
Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Texted-by: Thomas Zimmermann <tzimmermann@...e.de>
If no other reviews come in, I'll merge the patch by the end of the week.
Best regards
Thomas
> ---
> v2:
> - Rebased to the latest drm-misc-next branch. [2]
> - Updated patch log to match the base code.
>
> v1: https://lore.kernel.org/all/20240909051529.26776-1-yan.y.zhao@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 69c5f65e9853..9055b1dd66df 100644
> --- a/drivers/gpu/drm/tiny/bochs.c
> +++ b/drivers/gpu/drm/tiny/bochs.c
> @@ -268,7 +268,7 @@ static int bochs_hw_init(struct bochs_device *bochs)
> if (!devm_request_mem_region(&pdev->dev, addr, size, "bochs-drm"))
> DRM_WARN("Cannot request framebuffer, boot fb still active?\n");
>
> - bochs->fb_map = devm_ioremap(&pdev->dev, addr, size);
> + bochs->fb_map = devm_ioremap_wc(&pdev->dev, 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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