2021-11-16 23:16:12

by Georgi Djakov

Subject: [RFC 2/2] drm/msm/gem: Make use of the system cache

Instead of writing to WC cmdstream buffers that go all the way to the main
memory, let's use the system cache to improve the performance.

Signed-off-by: Georgi Djakov <[email protected]>
---
drivers/gpu/drm/msm/msm_gem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 104fdfc14027..921a1c24721e 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -214,7 +214,7 @@ void msm_gem_put_pages(struct drm_gem_object *obj)
static pgprot_t msm_gem_pgprot(struct msm_gem_object *msm_obj, pgprot_t prot)
{
if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
- return pgprot_writecombine(prot);
+ return pgprot_syscached(prot);
return prot;
}

2021-11-17 07:38:18

by Arnd Bergmann

Subject: Re: [RFC 2/2] drm/msm/gem: Make use of the system cache

On Wed, Nov 17, 2021 at 12:16 AM Georgi Djakov
<[email protected]> wrote:
>
> Instead of writing to WC cmdstream buffers that go all the way to the main
> memory, let's use the system cache to improve the performance.
>
> Signed-off-by: Georgi Djakov <[email protected]>
> ---
> drivers/gpu/drm/msm/msm_gem.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> index 104fdfc14027..921a1c24721e 100644
> --- a/drivers/gpu/drm/msm/msm_gem.c
> +++ b/drivers/gpu/drm/msm/msm_gem.c
> @@ -214,7 +214,7 @@ void msm_gem_put_pages(struct drm_gem_object *obj)
> static pgprot_t msm_gem_pgprot(struct msm_gem_object *msm_obj, pgprot_t prot)
> {
> if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
> - return pgprot_writecombine(prot);
> + return pgprot_syscached(prot);
> return prot;
> }

Based on the definition in patch 1, doesn't this mean that 32-bit
kernels degrade
from writecombined to uncached, making them a lot slower?

My feeling about this series is that there should be a clearer
definition of what
exactly happens on systems with and without system cache.

Arnd