Re: [PATCH v2 00/11] Proper GT TLB invalidation layering and new coalescing feature.

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Jul 09, 2024 at 10:57:14AM +0100, Matthew Auld wrote:
> Hi,
> 
> On 08/07/2024 05:03, Matthew Brost wrote:
> > While debuging [1] an issue was identified in which if too many GT TLB
> > invalidations are issued to the GuC, the GuC can get overwhelmed to the
> > point scheduling of jobs starts to stall. To avoid this, hold and
> > coalesce GT TLB invalidations in the KMD if a watermark of pending
> > invalidations is past. Add gitlab for this issue has also been opened
> > [2].
> > 
> > Layering issues with GT TLB invalidations are known [3] which needed to
> > be fixed first before adding this new feature.
> > 
> > - Patches 1-8 fix the layering.
> > - Patches 9-11 add coalescing feature.
> > 
> > We could merge these two as seperate series if needed.
> > 
> > CCing various stakeholders (Farah, Michal, Nirmoy) which have raised GT
> > TLB invalidation issues in the past.
> 
> Maybe worth mentioning for [1], we try to process TLB invalidations directly
> from the irq, however we also only process the g2h queue in-order, so if
> there is something other than TLB invalidation or fault earlier in the queue

Faults get sunk to a secondary queue to avoid stalling the g2h queue +
work around dma-fencing rules.

> then we do nothing useful from the irq and just return, that is until the wq
> can eventually process those earlier items that couldn't be processed
> directly from the irq. In the past I have seen TLB timeouts where the TLB
> invalidation is clearly in the g2h queue (and has been for a while), but is
> stuck behind something earlier in the queue that needs the wq, but system is
> under such a heavy load that the wq can't be scheduled in a timely manner.
> 

Great point. Will add.

But perhaps we need to change the 'ct->g2h_wq' priority too. I think
this should be the highest priority WQ in the Xe KMD.

Thanks,
Matt

> > 
> > v2:
> >   - Fix CI issues
> >   - Clean up some of the series / patch structure
> > 
> > Matt
> > 
> > [1] https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/799#note_2449497
> > [2] https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2162
> > [3] https://patchwork.freedesktop.org/series/133001/
> > 
> > Matthew Brost (11):
> >    drm/xe: Add xe_gt_tlb_invalidation_fence_init helper
> >    drm/xe: Drop xe_gt_tlb_invalidation_wait
> >    drm/xe: s/tlb_invalidation.lock/tlb_invalidation.fence_lock
> >    drm/xe: Add tlb_invalidation.seqno_lock
> >    drm/xe: Add xe_gt_tlb_invalidation_done_handler
> >    drm/xe: Add send tlb invalidation helpers
> >    drm/xe: Add xe_guc_tlb_invalidation layer
> >    drm/xe: Add multi-client support for GT TLB invalidations
> >    drm/xe: Add GT TLB invalidation coalescing
> >    drm/xe: Add GT TLB invalidation coalesce tracepoints
> >    drm/xe: Add GT TLB invalidation watermark debugfs
> > 
> >   drivers/gpu/drm/xe/Makefile                   |   1 +
> >   drivers/gpu/drm/xe/xe_debugfs.c               |  38 ++
> >   drivers/gpu/drm/xe/xe_device.c                |   3 +
> >   drivers/gpu/drm/xe/xe_device_types.h          |   5 +
> >   drivers/gpu/drm/xe/xe_ggtt.c                  |  21 +-
> >   drivers/gpu/drm/xe/xe_ggtt_types.h            |   5 +
> >   drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c   | 641 ++++++++++++------
> >   drivers/gpu/drm/xe/xe_gt_tlb_invalidation.h   |  26 +-
> >   .../gpu/drm/xe/xe_gt_tlb_invalidation_types.h |  41 ++
> >   drivers/gpu/drm/xe/xe_gt_types.h              |  43 +-
> >   drivers/gpu/drm/xe/xe_guc_ct.c                |   2 +-
> >   drivers/gpu/drm/xe/xe_guc_tlb_invalidation.c  | 145 ++++
> >   drivers/gpu/drm/xe/xe_guc_tlb_invalidation.h  |  18 +
> >   drivers/gpu/drm/xe/xe_pt.c                    |  33 +-
> >   drivers/gpu/drm/xe/xe_trace.h                 |  10 +
> >   drivers/gpu/drm/xe/xe_vm.c                    |  45 +-
> >   drivers/gpu/drm/xe/xe_vm_types.h              |   3 +
> >   17 files changed, 801 insertions(+), 279 deletions(-)
> >   create mode 100644 drivers/gpu/drm/xe/xe_guc_tlb_invalidation.c
> >   create mode 100644 drivers/gpu/drm/xe/xe_guc_tlb_invalidation.h
> >