With multi-device we are much more likely to have multiple drm-gpusvm ranges pointing to the same struct mm range.
To avoid calling into drm_pagemap_populate_mm(), which is always very costly, introduce a much less costly drm_gpusvm function, drm_gpusvm_scan_mm() to scan the current migration state. The device fault-handler and prefetcher can use this function to determine whether migration is really necessary. There are a couple of performance improvements that can be done for this function if it turns out to be too costly. Those are documented in the code. v3: - New patch. Signed-off-by: Thomas Hellström <[email protected]> --- drivers/gpu/drm/drm_gpusvm.c | 121 +++++++++++++++++++++++++++++++++++ include/drm/drm_gpusvm.h | 29 +++++++++ 2 files changed, 150 insertions(+) diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c index 4c7474a331bc..aa9a0b60e727 100644 --- a/drivers/gpu/drm/drm_gpusvm.c +++ b/drivers/gpu/drm/drm_gpusvm.c @@ -743,6 +743,127 @@ static bool drm_gpusvm_check_pages(struct drm_gpusvm *gpusvm, return err ? false : true; } +/** + * drm_gpusvm_scan_mm() - Check the migration state of a drm_gpusvm_range + * @range: Pointer to the struct drm_gpusvm_range to check. + * @dev_private_owner: The struct dev_private_owner to use to determine + * compatible device-private pages. + * @pagemap: The struct dev_pagemap pointer to use for pagemap-specific + * checks. + * + * Scan the CPU address space corresponding to @range and return the + * current migration state. Note that the result may be invalid as + * soon as the function returns. It's an advisory check. + * + * TODO: Bail early and call hmm_range_fault() for subranges. + * + * Return: See &enum drm_gpusvm_scan_result. + */ +enum drm_gpusvm_scan_result drm_gpusvm_scan_mm(struct drm_gpusvm_range *range, + void *dev_private_owner, + const struct dev_pagemap *pagemap) +{ + struct mmu_interval_notifier *notifier = &range->notifier->notifier; + unsigned long start = drm_gpusvm_range_start(range); + unsigned long end = drm_gpusvm_range_end(range); + struct hmm_range hmm_range = { + .default_flags = 0, + .notifier = notifier, + .start = start, + .end = end, + .dev_private_owner = dev_private_owner, + }; + unsigned long timeout = + jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT); + enum drm_gpusvm_scan_result state = DRM_GPUSVM_SCAN_UNPOPULATED, new_state; + unsigned long *pfns; + unsigned long npages = npages_in_range(start, end); + const struct dev_pagemap *other = NULL; + int err, i; + + pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL); + if (!pfns) + return DRM_GPUSVM_SCAN_UNPOPULATED; + + hmm_range.hmm_pfns = pfns; + +retry: + hmm_range.notifier_seq = mmu_interval_read_begin(notifier); + mmap_read_lock(range->gpusvm->mm); + + while (true) { + err = hmm_range_fault(&hmm_range); + if (err == -EBUSY) { + if (time_after(jiffies, timeout)) + break; + + hmm_range.notifier_seq = + mmu_interval_read_begin(notifier); + continue; + } + break; + } + mmap_read_unlock(range->gpusvm->mm); + if (err) + goto err_free; + + drm_gpusvm_notifier_lock(range->gpusvm); + if (mmu_interval_read_retry(notifier, hmm_range.notifier_seq)) { + drm_gpusvm_notifier_unlock(range->gpusvm); + goto retry; + } + + for (i = 0; i < npages;) { + struct page *page; + const struct dev_pagemap *cur = NULL; + + if (!(pfns[i] & HMM_PFN_VALID)) { + state = DRM_GPUSVM_SCAN_UNPOPULATED; + goto err_free; + } + + page = hmm_pfn_to_page(pfns[i]); + if (is_device_private_page(page) || + is_device_coherent_page(page)) + cur = page_pgmap(page); + + if (cur == pagemap) { + new_state = DRM_GPUSVM_SCAN_EQUAL; + } else if (cur && (cur == other || !other)) { + new_state = DRM_GPUSVM_SCAN_OTHER; + other = cur; + } else if (cur) { + new_state = DRM_GPUSVM_SCAN_MIXED_DEVICE; + } else { + new_state = DRM_GPUSVM_SCAN_SYSTEM; + } + + /* + * TODO: Could use an array for state + * transitions, and caller might want it + * to bail early for some results. + */ + if (state == DRM_GPUSVM_SCAN_UNPOPULATED) { + state = new_state; + } else if (state != new_state) { + if (new_state == DRM_GPUSVM_SCAN_SYSTEM || + state == DRM_GPUSVM_SCAN_SYSTEM) + state = DRM_GPUSVM_SCAN_MIXED; + else if (state != DRM_GPUSVM_SCAN_MIXED) + state = DRM_GPUSVM_SCAN_MIXED_DEVICE; + } + + i += 1ul << drm_gpusvm_hmm_pfn_to_order(pfns[i], i, npages); + } + +err_free: + drm_gpusvm_notifier_unlock(range->gpusvm); + + kvfree(pfns); + return state; +} +EXPORT_SYMBOL(drm_gpusvm_scan_mm); + /** * drm_gpusvm_range_chunk_size() - Determine chunk size for GPU SVM range * @gpusvm: Pointer to the GPU SVM structure diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h index 632e100e6efb..2578ac92a8d4 100644 --- a/include/drm/drm_gpusvm.h +++ b/include/drm/drm_gpusvm.h @@ -328,6 +328,35 @@ void drm_gpusvm_free_pages(struct drm_gpusvm *gpusvm, struct drm_gpusvm_pages *svm_pages, unsigned long npages); +/** + * enum drm_gpusvm_scan_result - Scan result from the drm_gpusvm_scan_mm() function. + * @DRM_GPUSVM_SCAN_UNPOPULATED: At least one page was not present or inaccessible. + * @DRM_GPUSVM_SCAN_EQUAL: All pages belong to the struct dev_pagemap indicated as + * the @pagemap argument to the drm_gpusvm_scan_mm() function. + * @DRM_GPUSVM_SCAN_OTHER: All pages belong to exactly one dev_pagemap, which is + * *NOT* the @pagemap argument to the drm_gpusvm_scan_mm(). All pages belong to + * the same device private owner. + * @DRM_GPUSVM_SCAN_SYSTEM: All pages are present and system pages. + * @DRM_GPUSVM_SCAN_MIXED_DEVICE: All pages are device pages and belong to at least + * two different struct dev_pagemaps. All pages belong to the same device private + * owner. + * @DRM_GPUSVM_SCAN_MIXED: Pages are present and are a mix of system pages + * and device-private pages. All device-private pages belong to the same device + * private owner. + */ +enum drm_gpusvm_scan_result { + DRM_GPUSVM_SCAN_UNPOPULATED, + DRM_GPUSVM_SCAN_EQUAL, + DRM_GPUSVM_SCAN_OTHER, + DRM_GPUSVM_SCAN_SYSTEM, + DRM_GPUSVM_SCAN_MIXED_DEVICE, + DRM_GPUSVM_SCAN_MIXED, +}; + +enum drm_gpusvm_scan_result drm_gpusvm_scan_mm(struct drm_gpusvm_range *range, + void *dev_private_owner, + const struct dev_pagemap *pagemap); + #ifdef CONFIG_LOCKDEP /** * drm_gpusvm_driver_set_lock() - Set the lock protecting accesses to GPU SVM -- 2.51.1
