<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style> </head> <body dir="ltr"> <div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"> The snoop bit is for snooping the CPU cache by the GPU when doing system memory mappings. </div> <div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"> </div> <div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"> Alex </div> <div id="appendonsend"></div> <hr style="display:inline-block;width:98%" tabindex="-1"> <div id="divRplyFwdMsg" dir="ltr">From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> on behalf of Zeng, Oak <Oak.Zeng@amd.com> Sent: Thursday, August 8, 2019 12:02 PM To: Koenig, Christian <Christian.Koenig@amd.com>; amd-gfx@lists.freedesktop.org <amd-gfx@lists.freedesktop.org> Cc: Kuehling, Felix <Felix.Kuehling@amd.com>; Keely, Sean <Sean.Keely@amd.com> Subject: RE: [PATCH 1/5] drm/amdgpu: Extends amdgpu vm definitions <div> </div> </div> <div class="BodyFragment"> <div class="PlainText">Hi Christian, My understanding of the snoop bit (C bit in the PTE definition) is to probe remote gpu's L2 cache after this gpu write remote gpu's vram. Is this correct? I am still checking this point with HW engineer. If this is correct, then the snooping (or probing) is a way to maintain certain cache coherency when one memory is access by two masters (for example two gpu). With existing AMDGPU_VM_ definitions in amdgpu_drm.h, how does a user implement the request like: I want a trunk of vram physically in a remote gpu, I want to access it in a uncached way (AMDGPU_VM_MTYPE_UC) but I want to probe remote gpu's cache when I modify this vram. >From PTE's definition, both C bit and mtype and R/W/X bits are just flags to enable user to program page access behavior. Any detail reason why we shouldn't expose the snoop bit? Regards, Oak -----Original Message----- From: Christian König <ckoenig.leichtzumerken@gmail.com> Sent: Wednesday, August 7, 2019 4:42 AM To: Zeng, Oak <Oak.Zeng@amd.com>; amd-gfx@lists.freedesktop.org Cc: Kuehling, Felix <Felix.Kuehling@amd.com>; Koenig, Christian <Christian.Koenig@amd.com>; Keely, Sean <Sean.Keely@amd.com> Subject: Re: [PATCH 1/5] drm/amdgpu: Extends amdgpu vm definitions Am 07.08.19 um 04:31 schrieb Zeng, Oak: > Add definition of all supported mtypes. The RW mtype is recently > introduced for arcturus. Also add definition for the > cachable/snoopable bit, which will be used later in this series. > > Change-Id: I96fc9bb4b6b1e62bdc10b600d8aaa6a802128d6d > Signed-off-by: Oak Zeng <Oak.Zeng@amd.com> > --- > drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 9 +++++++-- > include/uapi/drm/amdgpu_drm.h | 4 ++++ > 2 files changed, 11 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h > b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h > index 2eda3a8..7a77477 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h > @@ -80,8 +80,13 @@ struct amdgpu_bo_list_entry; > #define AMDGPU_PTE_MTYPE_VG10(a) ((uint64_t)(a) << 57) > #define AMDGPU_PTE_MTYPE_VG10_MASK AMDGPU_PTE_MTYPE_VG10(3ULL) > > -#define AMDGPU_MTYPE_NC 0 > -#define AMDGPU_MTYPE_CC 2 > +enum amdgpu_mtype { > + AMDGPU_MTYPE_NC = 0, > + AMDGPU_MTYPE_WC = 1, > + AMDGPU_MTYPE_CC = 2, > + AMDGPU_MTYPE_UC = 3, > + AMDGPU_MTYPE_RW = 4, > +}; > > #define AMDGPU_PTE_DEFAULT_ATC (AMDGPU_PTE_SYSTEM \ > | AMDGPU_PTE_SNOOPED \ > diff --git a/include/uapi/drm/amdgpu_drm.h > b/include/uapi/drm/amdgpu_drm.h index ca97b68..2889663 100644 > --- a/include/uapi/drm/amdgpu_drm.h > +++ b/include/uapi/drm/amdgpu_drm.h > @@ -503,6 +503,10 @@ struct drm_amdgpu_gem_op { > #define AMDGPU_VM_MTYPE_CC (3 << 5) > /* Use UC MTYPE instead of default MTYPE */ > #define AMDGPU_VM_MTYPE_UC (4 << 5) > +/* Use RW MTYPE instead of default MTYPE */ > +#define AMDGPU_VM_MTYPE_RW (5 << 5) > +/* Cacheable/snoopable */ > +#define AMDGPU_VM_PAGE_SNOOPED (1 << 9) That's a rather big NAK. Cache snooping is not something userspace is allowed to be aware of. Christian. > > struct drm_amdgpu_gem_va { > /** GEM object handle */ _______________________________________________ amd-gfx mailing list amd-gfx@lists.freedesktop.org <a href="https://lists.freedesktop.org/mailman/listinfo/amd-gfx">https://lists.freedesktop.org/mailman/listinfo/amd-gfx</a></div> </div> </body> </html>