<!DOCTYPE html><html><head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body> Hi Thomas, <div class="moz-cite-prefix">On 8/26/2024 10:36 AM, Thomas Hellström wrote: </div> <blockquote type="cite" cite="mid:e76049b03dca87599346ec1db3ac6bfec97efee3.camel@linux.intel.com"> <pre wrap="" class="moz-quote-pre">On Mon, 2024-08-26 at 10:26 +0200, Nirmoy Das wrote: </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">Hi Thomas, On 8/23/2024 11:38 AM, Thomas Hellström wrote: </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">Hi, Nirmoy, On Thu, 2024-08-22 at 14:42 +0200, Nirmoy Das wrote: </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">Implement GPU clear-on-free for pooled system pages in Xe. Ensure proper use of TTM_TT_FLAG_CLEARED_ON_FREE by leveraging ttm_device_funcs.release_notify() for GPU clear-on-free. If GPU clear fails, xe_ttm_tt_unpopulate() will fallback to CPU clear. Clear-on-free is only relevant for pooled pages as driver needs to give back those pages. So do clear-on-free only for such BOs and keep doing clear-on-alloc for ttm_cached type BOs Cc: Matthew Auld <a class="moz-txt-link-rfc2396E" href="mailto:matthew.auld@intel.com"><matthew.auld@intel.com></a> Cc: Matthew Brost <a class="moz-txt-link-rfc2396E" href="mailto:matthew.brost@intel.com"><matthew.brost@intel.com></a> Cc: Thomas Hellström <a class="moz-txt-link-rfc2396E" href="mailto:thomas.hellstrom@linux.intel.com"><thomas.hellstrom@linux.intel.com></a> Signed-off-by: Nirmoy Das <a class="moz-txt-link-rfc2396E" href="mailto:nirmoy.das@intel.com"><nirmoy.das@intel.com></a> </pre> </blockquote> <pre wrap="" class="moz-quote-pre">While this would probably work, I don't immediately see the benefit over CPU clearing, since we have no way of combining this with the CCS clear, right? </pre> </blockquote> <pre wrap="" class="moz-quote-pre"> If XE/ttm could do clear-on-free(data+CCS) with GPU all the time then I think we could skip ccs clearing on alloc, assuming only GPU access modifies a CCS state and on boot CCS region is zeroed. I think that can't be guaranteed so we have to clear ccs on alloc. I agree, there won't be much latency benefit of doing clear-on-free for ccs devices. I will still try to run some tests to validate it, I have done that for this RFC.</pre> </blockquote> </blockquote> s/have done/haven't done <blockquote type="cite" cite="mid:e76049b03dca87599346ec1db3ac6bfec97efee3.camel@linux.intel.com"> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre"> </pre> </blockquote> <pre wrap="" class="moz-quote-pre"> OK, yes this would probably work. Do we need to clear all CCS on module load or can we safely assume that no useful info is left in the CCS memory at that time?</pre> </blockquote> I tried to find some info on this but I don't see any mention of initial state of CCS state memory at boot. I think, currently we are safe as we do clear clearing on alloc so even if something is left out, UMD will never see it. <blockquote type="cite" cite="mid:e76049b03dca87599346ec1db3ac6bfec97efee3.camel@linux.intel.com"> <pre wrap="" class="moz-quote-pre"> </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre"> I've discussed this with Ron and it seems there is on going conversation if there is a way to avoid ccs clearing if data is zeroed. Let's see how that goes. </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre"> So the clearing latency will most probably be increased, but the bo releasing thread won't see that because the waiting for clear is offloaded to the TTM delayed destroy mechanism. Also, once we've dropped the gem refcount to zero, the gem members of the object, including bo_move, are strictly not valid anymore and shouldn't be used. </pre> </blockquote> <pre wrap="" class="moz-quote-pre"> Could you please expand this? I am not seeing the connection between bo_move and refcount. Are you saying release_notify is not the right place to do this ? </pre> </blockquote> <pre wrap="" class="moz-quote-pre"> Yes. At release_notify, the gem refcount has dropped to zero, and we don't allow calling bo_move at that point, as the driver might want to do some cleanup in the gem_release before putting the last ttm_bo reference.</pre> </blockquote> What should be the correct place do clear pool pages if we plan to do this in future ? Regards, Nirmoy <blockquote type="cite" cite="mid:e76049b03dca87599346ec1db3ac6bfec97efee3.camel@linux.intel.com"> <pre wrap="" class="moz-quote-pre"> Thanks, Thomas </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre"> </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">If we want to try to improve freeing latency by offloading the clearing on free to a separate CPU thread, though, maybe we could discuss with Christian to always (or if a flag in the ttm device requests it) take the TTM delayed destruction path for bos with pooled pages, rather than to free them sync, something along the lines of: diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c index 320592435252..fca69ec1740d 100644 --- a/drivers/gpu/drm/ttm/ttm_bo.c +++ b/drivers/gpu/drm/ttm/ttm_bo.c @@ -271,7 +271,7 @@ static void ttm_bo_release(struct kref *kref) if (!dma_resv_test_signaled(bo->base.resv, DMA_RESV_USAGE_BOOKKEEP) || - (want_init_on_free() && (bo->ttm != NULL)) || + (bo->ttm && (want_init_on_free() || bo->ttm- </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">caching != ttm_cached)) || </pre> </blockquote> <pre wrap="" class="moz-quote-pre"> bo->type == ttm_bo_type_sg || !dma_resv_trylock(bo->base.resv)) { /* The BO is not idle, resurrect it for delayed destroy */ Would ofc require some substantial proven latency gain, though. Overall system cpu usage would probably not improve. </pre> </blockquote> <pre wrap="" class="moz-quote-pre"> I will run some tests with the above change and get back. Thanks, Nirmoy </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre"> /Thomas </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">--- drivers/gpu/drm/xe/xe_bo.c | 101 +++++++++++++++++++++++++++++++++-- -- 1 file changed, 91 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c index 6ed0e1955215..e7bc74f8ae82 100644 --- a/drivers/gpu/drm/xe/xe_bo.c +++ b/drivers/gpu/drm/xe/xe_bo.c @@ -283,6 +283,8 @@ struct xe_ttm_tt { struct device *dev; struct sg_table sgt; struct sg_table *sg; + bool sys_clear_on_free; + bool sys_clear_on_alloc; }; static int xe_tt_map_sg(struct ttm_tt *tt) @@ -401,8 +403,23 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, * flag. Zeroed pages are only required for ttm_bo_type_device so * unwanted data is not leaked to userspace. */ - if (ttm_bo->type == ttm_bo_type_device && xe- </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">mem.gpu_page_clear_sys) </pre> </blockquote> <pre wrap="" class="moz-quote-pre">- page_flags |= TTM_TT_FLAG_CLEARED_ON_FREE; + if (ttm_bo->type == ttm_bo_type_device && xe- </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">mem.gpu_page_clear_sys) { </pre> </blockquote> <pre wrap="" class="moz-quote-pre">+ /* + * Non-pooled BOs are always clear on alloc when possible. + * clear-on-free is not needed as there is no pool to give pages back. + */ + if (caching == ttm_cached) { + tt->sys_clear_on_alloc = true; + tt->sys_clear_on_free = false; + } else { + /* + * For pooled BO, clear-on-alloc is done by the CPU for now and + * GPU will do clear on free when releasing the BO. + */ + tt->sys_clear_on_alloc = false; + tt->sys_clear_on_free = true; + } + } err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching, extra_pages); if (err) { @@ -416,8 +433,10 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo, static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt, struct ttm_operation_ctx *ctx) { + struct xe_ttm_tt *xe_tt; int err; + xe_tt = container_of(tt, struct xe_ttm_tt, ttm); /* * dma-bufs are not populated with pages, and the dma- * addresses are set up when moved to XE_PL_TT. @@ -426,7 +445,7 @@ static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt, return 0; /* Clear TTM_TT_FLAG_ZERO_ALLOC when GPU is set to clear system pages */ - if (tt->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE) + if (xe_tt->sys_clear_on_alloc) tt->page_flags &= ~TTM_TT_FLAG_ZERO_ALLOC; err = ttm_pool_alloc(&ttm_dev->pool, tt, ctx); @@ -438,11 +457,19 @@ static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt, static void xe_ttm_tt_unpopulate(struct ttm_device *ttm_dev, struct ttm_tt *tt) { + struct xe_ttm_tt *xe_tt; + + xe_tt = container_of(tt, struct xe_ttm_tt, ttm); + if (tt->page_flags & TTM_TT_FLAG_EXTERNAL) return; xe_tt_unmap_sg(tt); + /* Hint TTM pool that pages are already cleared */ + if (xe_tt->sys_clear_on_free) + tt->page_flags |= TTM_TT_FLAG_CLEARED_ON_FREE; + return ttm_pool_free(&ttm_dev->pool, tt); } @@ -664,6 +691,7 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict, struct ttm_resource *old_mem = ttm_bo->resource; u32 old_mem_type = old_mem ? old_mem->mem_type : XE_PL_SYSTEM; struct ttm_tt *ttm = ttm_bo->ttm; + struct xe_ttm_tt *xe_tt; struct xe_migrate *migrate = NULL; struct dma_fence *fence; bool move_lacks_source; @@ -674,12 +702,13 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict, bool clear_system_pages; int ret = 0; + xe_tt = container_of(ttm_bo->ttm, struct xe_ttm_tt, ttm); /* * Clear TTM_TT_FLAG_CLEARED_ON_FREE on bo creation path when * moving to system as the bo doesn't have dma_mapping. */ if (!old_mem && ttm && !ttm_tt_is_populated(ttm)) - ttm->page_flags &= ~TTM_TT_FLAG_CLEARED_ON_FREE; + xe_tt->sys_clear_on_alloc = false; /* Bo creation path, moving to system or TT. */ if ((!old_mem && ttm) && !handle_system_ccs) { @@ -703,10 +732,9 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict, move_lacks_source = handle_system_ccs ? (!bo- </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">ccs_cleared) </pre> </blockquote> <pre wrap="" class="moz-quote-pre">: (!mem_type_is_vr am(o ld_mem_type) && !tt_has_data); - clear_system_pages = ttm && (ttm->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE); + clear_system_pages = ttm && xe_tt->sys_clear_on_alloc; needs_clear = (ttm && ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) || - (!ttm && ttm_bo->type == ttm_bo_type_device) || - clear_system_pages; + (!ttm && ttm_bo->type == ttm_bo_type_device) || clear_system_pages; if (new_mem->mem_type == XE_PL_TT) { ret = xe_tt_map_sg(ttm); @@ -1028,10 +1056,47 @@ static bool xe_ttm_bo_lock_in_destructor(struct ttm_buffer_object *ttm_bo) return locked; } +static struct dma_fence *xe_ttm_bo_clear_on_free(struct ttm_buffer_object *ttm_bo) +{ + struct xe_bo *bo = ttm_to_xe_bo(ttm_bo); + struct xe_device *xe = xe_bo_device(bo); + struct xe_migrate *migrate; + struct xe_ttm_tt *xe_tt; + struct dma_fence *clear_fence; + + /* return early if nothing to clear */ + if (!ttm_bo->ttm) + return NULL; + + xe_tt = container_of(ttm_bo->ttm, struct xe_ttm_tt, ttm); + /* return early if nothing to clear */ + if (!xe_tt->sys_clear_on_free || !bo->ttm.resource) + return NULL; + + if (XE_WARN_ON(!xe_tt->sg)) + return NULL; + + if (bo->tile) + migrate = bo->tile->migrate; + else + migrate = xe->tiles[0].migrate; + + xe_assert(xe, migrate); + + clear_fence = xe_migrate_clear(migrate, bo, bo- </pre> <blockquote type="cite"> <pre wrap="" class="moz-quote-pre">ttm.resource, </pre> </blockquote> <pre wrap="" class="moz-quote-pre">+ XE_MIGRATE_CLEAR_FLAG_FULL); + if (IS_ERR(clear_fence)) + return NULL; + + xe_tt->sys_clear_on_free = false; + + return clear_fence; +} + static void xe_ttm_bo_release_notify(struct ttm_buffer_object *ttm_bo) { struct dma_resv_iter cursor; - struct dma_fence *fence; + struct dma_fence *clear_fence, *fence; struct dma_fence *replacement = NULL; struct xe_bo *bo; @@ -1041,15 +1106,31 @@ static void xe_ttm_bo_release_notify(struct ttm_buffer_object *ttm_bo) bo = ttm_to_xe_bo(ttm_bo); xe_assert(xe_bo_device(bo), !(bo->created && kref_read(&ttm_bo->base.refcount))); + clear_fence = xe_ttm_bo_clear_on_free(ttm_bo); + /* * Corner case where TTM fails to allocate memory and this BOs resv * still points the VMs resv */ - if (ttm_bo->base.resv != &ttm_bo->base._resv) + if (ttm_bo->base.resv != &ttm_bo->base._resv) { + if (clear_fence) + dma_fence_wait(clear_fence, false); return; + } - if (!xe_ttm_bo_lock_in_destructor(ttm_bo)) + if (!xe_ttm_bo_lock_in_destructor(ttm_bo)) { + if (clear_fence) + dma_fence_wait(clear_fence, false); return; + } + + if (clear_fence) { + if (dma_resv_reserve_fences(ttm_bo->base.resv, 1)) + dma_fence_wait(clear_fence, false); + else + dma_resv_add_fence(ttm_bo->base.resv, clear_fence, + DMA_RESV_USAGE_KERNEL); + } /* * Scrub the preempt fences if any. The unbind fence is already </pre> </blockquote> </blockquote> </blockquote> <pre wrap="" class="moz-quote-pre"> </pre> </blockquote> </body> </html>