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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAK8P3a3W13wb5B_FMSCEp0JTUFrPk=Fp8N59oa58wxn+WeTroA@mail.gmail.com>
Date:   Wed, 17 Nov 2021 08:37:58 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Georgi Djakov <quic_c_gdjako@...cinc.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>,
        Robin Murphy <robin.murphy@....com>,
        Marc Zyngier <maz@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>
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
<quic_c_gdjako@...cinc.com> 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 <quic_c_gdjako@...cinc.com>
> ---
>  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