Re: [PATCH v6 2/2] drm/xe/lnl: Offload system clear page activity to GPU

[Matthew Auld <matthew.auld@intel.com>]

On 16/08/2024 14:51, Nirmoy Das wrote:
> On LNL because of flat CCS, driver creates migrates job to clear
> CCS meta data. Extend that to also clear system pages using GPU.
> Inform TTM to allocate pages without __GFP_ZERO to avoid double page
> clearing by clearing out TTM_TT_FLAG_ZERO_ALLOC flag and set
> TTM_TT_FLAG_CLEARED_ON_FREE while freeing to skip ttm pool's clear
> on free as XE now takes care of clearing pages. If a bo is in system
> placement such as BO created with  DRM_XE_GEM_CREATE_FLAG_DEFER_BACKING
> and there is a cpu map then for such BO gpu clear will be avoided as
> there is no dma mapping for such BO at that moment to create migration
> jobs.
> 
> Tested this patch api_overhead_benchmark_l0 from
> https://github.com/intel/compute-benchmarks
> 
> Without the patch:
> api_overhead_benchmark_l0 --testFilter=UsmMemoryAllocation:
> UsmMemoryAllocation(api=l0 type=Host size=4KB) 84.206 us
> UsmMemoryAllocation(api=l0 type=Host size=1GB) 105775.56 us
> erf tool top 5 entries:
> 71.44% api_overhead_be  [kernel.kallsyms]   [k] clear_page_erms
> 6.34%  api_overhead_be  [kernel.kallsyms]   [k] __pageblock_pfn_to_page
> 2.24%  api_overhead_be  [kernel.kallsyms]   [k] cpa_flush
> 2.15%  api_overhead_be  [kernel.kallsyms]   [k] pages_are_mergeable
> 1.94%  api_overhead_be  [kernel.kallsyms]   [k] find_next_iomem_res
> 
> With the patch:
> api_overhead_benchmark_l0 --testFilter=UsmMemoryAllocation:
> UsmMemoryAllocation(api=l0 type=Host size=4KB) 79.439 us
> UsmMemoryAllocation(api=l0 type=Host size=1GB) 98677.75 us
> Perf tool top 5 entries:
> 11.16% api_overhead_be  [kernel.kallsyms]   [k] __pageblock_pfn_to_page
> 7.85%  api_overhead_be  [kernel.kallsyms]   [k] cpa_flush
> 7.59%  api_overhead_be  [kernel.kallsyms]   [k] find_next_iomem_res
> 7.24%  api_overhead_be  [kernel.kallsyms]   [k] pages_are_mergeable
> 5.53%  api_overhead_be  [kernel.kallsyms]   [k] lookup_address_in_pgd_attr
> 
> Without this patch clear_page_erms() dominates execution time which is
> also not pipelined with migration jobs. With this patch page clearing
> will get pipelined with migration job and will free CPU for more work.
> 
> v2: Handle regression on dgfx(Himal)
>      Update commit message as no ttm API changes needed.
> v3: Fix Kunit test.
> v4: handle data leak on cpu mmap(Thomas)
> v5: s/gpu_page_clear/gpu_page_clear_sys and move setting
>      it to xe_ttm_sys_mgr_init() and other nits (Matt Auld)
> v6: Disable it when init_on_alloc and/or init_on_free is active(Matt)
>      Use compute-benchmarks as reporter used it to report this
>      allocation latency issue also a proper test application than mime.
>      In v5, the test showed significant reduction in alloc latency but
>      that is not the case any more, I think this was mostly because
>      previous test was done on IFWI which had low mem BW from CPU.
> 
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>

Reviewed-by: Matthew Auld <matthew.auld@intel.com>