Re: [PATCH 12/26] drm/xe/pf: Increase PF GuC Buffer Cache size and use it for VF migration

Michał Winiarski
2025-10-21T00:50:58Z

On Mon, Oct 13, 2025 at 01:27:55PM +0200, Michal Wajdeczko wrote:
>
>
> On 10/11/2025 9:38 PM, Michał Winiarski wrote:
> > Contiguous PF GGTT VMAs can be scarce after creating VFs.
> > Increase the GuC buffer cache size to 8M for PF so that we can fit GuC
> > migration data (which currently maxes out at just over 4M) and use the
> > cache instead of allocating fresh BOs.
> >
> > Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
> > ---
> > drivers/gpu/drm/xe/xe_gt_sriov_pf_migration.c | 54 +++++++------------
> > drivers/gpu/drm/xe/xe_guc.c | 2 +-
> > 2 files changed, 20 insertions(+), 36 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_pf_migration.c b/drivers/gpu/drm/xe/xe_gt_sriov_pf_migration.c
> > index 50f09994e2854..8b96eff8df93b 100644
> > --- a/drivers/gpu/drm/xe/xe_gt_sriov_pf_migration.c
> > +++ b/drivers/gpu/drm/xe/xe_gt_sriov_pf_migration.c
> > @@ -11,7 +11,7 @@
> > #include "xe_gt_sriov_pf_helpers.h"
> > #include "xe_gt_sriov_pf_migration.h"
> > #include "xe_gt_sriov_printk.h"
> > -#include "xe_guc.h"
> > +#include "xe_guc_buf.h"
> > #include "xe_guc_ct.h"
> > #include "xe_sriov.h"
> > #include "xe_sriov_pf_migration.h"
> > @@ -57,73 +57,57 @@ static int pf_send_guc_query_vf_state_size(struct xe_gt *gt, unsigned int vfid)
> >
> > /* Return: number of state dwords saved or a negative error code on failure */
> > static int pf_send_guc_save_vf_state(struct xe_gt *gt, unsigned int vfid,
> > - void *buff, size_t size)
> > + void *dst, size_t size)
> > {
> > const int ndwords = size / sizeof(u32);
> > - struct xe_tile *tile = gt_to_tile(gt);
> > - struct xe_device *xe = tile_to_xe(tile);
> > struct xe_guc *guc = &gt->uc.guc;
> > - struct xe_bo *bo;
> > + CLASS(xe_guc_buf, buf)(&guc->buf, ndwords);
> > int ret;
> >
> > xe_gt_assert(gt, size % sizeof(u32) == 0);
> > xe_gt_assert(gt, size == ndwords * sizeof(u32));
> >
> > - bo = xe_bo_create_pin_map_novm(xe, tile,
> > - ALIGN(size, PAGE_SIZE),
> > - ttm_bo_type_kernel,
> > - XE_BO_FLAG_SYSTEM |
> > - XE_BO_FLAG_GGTT |
> > - XE_BO_FLAG_GGTT_INVALIDATE, false);
> > - if (IS_ERR(bo))
> > - return PTR_ERR(bo);
> > + if (!xe_guc_buf_is_valid(buf))
> > + return -ENOBUFS;
> > +
> > + memset(xe_guc_buf_cpu_ptr(buf), 0, size);
>
> is that necessary? GuC will overwrite that anyway

It doesn't, so it actually is necessary.

>
> >
> > ret = guc_action_vf_save_restore(guc, vfid, GUC_PF_OPCODE_VF_SAVE,
> > - xe_bo_ggtt_addr(bo), ndwords);
> > - if (!ret)
> > + xe_guc_buf_flush(buf), ndwords);
> > + if (!ret) {
> > ret = -ENODATA;
> > - else if (ret > ndwords)
> > + } else if (ret > ndwords) {
> > ret = -EPROTO;
> > - else if (ret > 0)
> > - xe_map_memcpy_from(xe, buff, &bo->vmap, 0, ret * sizeof(u32));
> > + } else if (ret > 0) {
> > + xe_guc_buf_sync(buf);
> > + memcpy(dst, xe_guc_buf_cpu_ptr(buf), ret * sizeof(u32));
>
> with a small change suggested earlier, this could be just:
>
> memcpy(dst, xe_guc_buf_sync(buf), ret * sizeof(u32));

Ok.

>
> > + }
> >
> > - xe_bo_unpin_map_no_vm(bo);
> > return ret;
> > }
> >
> > /* Return: number of state dwords restored or a negative error code on failure */
> > static int pf_send_guc_restore_vf_state(struct xe_gt *gt, unsigned int vfid,
> > - const void *buff, size_t size)
> > + const void *src, size_t size)
> > {
> > const int ndwords = size / sizeof(u32);
> > - struct xe_tile *tile = gt_to_tile(gt);
> > - struct xe_device *xe = tile_to_xe(tile);
> > struct xe_guc *guc = &gt->uc.guc;
> > - struct xe_bo *bo;
> > + CLASS(xe_guc_buf_from_data, buf)(&guc->buf, src, size);
> > int ret;
> >
> > xe_gt_assert(gt, size % sizeof(u32) == 0);
> > xe_gt_assert(gt, size == ndwords * sizeof(u32));
> >
> > - bo = xe_bo_create_pin_map_novm(xe, tile,
> > - ALIGN(size, PAGE_SIZE),
> > - ttm_bo_type_kernel,
> > - XE_BO_FLAG_SYSTEM |
> > - XE_BO_FLAG_GGTT |
> > - XE_BO_FLAG_GGTT_INVALIDATE, false);
> > - if (IS_ERR(bo))
> > - return PTR_ERR(bo);
> > -
> > - xe_map_memcpy_to(xe, &bo->vmap, 0, buff, size);
> > + if (!xe_guc_buf_is_valid(buf))
> > + return -ENOBUFS;
> >
> > ret = guc_action_vf_save_restore(guc, vfid, GUC_PF_OPCODE_VF_RESTORE,
> > - xe_bo_ggtt_addr(bo), ndwords);
> > + xe_guc_buf_flush(buf), ndwords);
> > if (!ret)
> > ret = -ENODATA;
> > else if (ret > ndwords)
> > ret = -EPROTO;
> >
> > - xe_bo_unpin_map_no_vm(bo);
> > return ret;
> > }
> >
> > diff --git a/drivers/gpu/drm/xe/xe_guc.c b/drivers/gpu/drm/xe/xe_guc.c
> > index ccc7c60ae9b77..71ca06d1af62b 100644
> > --- a/drivers/gpu/drm/xe/xe_guc.c
> > +++ b/drivers/gpu/drm/xe/xe_guc.c
> > @@ -857,7 +857,7 @@ int xe_guc_init_post_hwconfig(struct xe_guc *guc)
> > if (ret)
> > return ret;
> >
> > - ret = xe_guc_buf_cache_init(&guc->buf, SZ_8K);
> > + ret = xe_guc_buf_cache_init(&guc->buf, IS_SRIOV_PF(guc_to_xe(guc)) ? SZ_8M : SZ_8K);
>
> shouldn't we also check for xe_sriov_pf_migration_supported() ?

Ok.

>
> also, shouldn't we get this SZ_8M somewhere from the PF code?
> and maybe PF could (one day) query that somehow from the GuC?

I'll start a discussion, but for now we'll stick to hardcoded max.
And it turns out it's just shy of 4M, so I'll reduce the size to SZ_4M.

-Michał

>
>
> > if (ret)
> > return ret;
> >
>