From: Adrian Huang ahuang12@lenovo.com
[ Upstream commit 3710e2b056cb92ad816e4d79fa54a6a5b6ad8cbd ]
When running the fio test on a 448-core AMD server + a NVME disk, a soft lockup or a hard lockup call trace is shown:
[soft lockup] watchdog: BUG: soft lockup - CPU#126 stuck for 23s! [swapper/126:0] RIP: 0010:_raw_spin_unlock_irqrestore+0x21/0x50 ... Call Trace: <IRQ> fq_flush_timeout+0x7d/0xd0 ? __pfx_fq_flush_timeout+0x10/0x10 call_timer_fn+0x2e/0x150 run_timer_softirq+0x48a/0x560 ? __pfx_fq_flush_timeout+0x10/0x10 ? clockevents_program_event+0xaf/0x130 __do_softirq+0xf1/0x335 irq_exit_rcu+0x9f/0xd0 sysvec_apic_timer_interrupt+0xb4/0xd0 </IRQ> <TASK> asm_sysvec_apic_timer_interrupt+0x1f/0x30 ...
Obvisouly, fq_flush_timeout spends over 20 seconds. Here is ftrace log:
| fq_flush_timeout() { | fq_ring_free() { | put_pages_list() { 0.170 us | free_unref_page_list(); 0.810 us | } | free_iova_fast() { | free_iova() { * 85622.66 us | _raw_spin_lock_irqsave(); 2.860 us | remove_iova(); 0.600 us | _raw_spin_unlock_irqrestore(); 0.470 us | lock_info_report(); 2.420 us | free_iova_mem.part.0(); * 85638.27 us | } * 85638.84 us | } | put_pages_list() { 0.230 us | free_unref_page_list(); 0.470 us | } ... ... $ 31017069 us | }
Most of cores are under lock contention for acquiring iova_rbtree_lock due to the iova flush queue mechanism.
[hard lockup] NMI watchdog: Watchdog detected hard LOCKUP on cpu 351 RIP: 0010:native_queued_spin_lock_slowpath+0x2d8/0x330
Call Trace: <IRQ> _raw_spin_lock_irqsave+0x4f/0x60 free_iova+0x27/0xd0 free_iova_fast+0x4d/0x1d0 fq_ring_free+0x9b/0x150 iommu_dma_free_iova+0xb4/0x2e0 __iommu_dma_unmap+0x10b/0x140 iommu_dma_unmap_sg+0x90/0x110 dma_unmap_sg_attrs+0x4a/0x50 nvme_unmap_data+0x5d/0x120 [nvme] nvme_pci_complete_batch+0x77/0xc0 [nvme] nvme_irq+0x2ee/0x350 [nvme] ? __pfx_nvme_pci_complete_batch+0x10/0x10 [nvme] __handle_irq_event_percpu+0x53/0x1a0 handle_irq_event_percpu+0x19/0x60 handle_irq_event+0x3d/0x60 handle_edge_irq+0xb3/0x210 __common_interrupt+0x7f/0x150 common_interrupt+0xc5/0xf0 </IRQ> <TASK> asm_common_interrupt+0x2b/0x40 ...
ftrace shows fq_ring_free spends over 10 seconds [1]. Again, most of cores are under lock contention for acquiring iova_rbtree_lock due to the iova flush queue mechanism.
[Root Cause] The root cause is that the max_hw_sectors_kb of nvme disk (mdts=10) is 4096kb, which streaming DMA mappings cannot benefit from the scalable IOVA mechanism introduced by the commit 9257b4a206fc ("iommu/iova: introduce per-cpu caching to iova allocation") if the length is greater than 128kb.
To fix the lock contention issue, clamp max_hw_sectors based on DMA optimized limitation in order to leverage scalable IOVA mechanism.
Note: The issue does not happen with another NVME disk (mdts = 5 and max_hw_sectors_kb = 128)
[1] https://gist.github.com/AdrianHuang/bf8ec7338204837631fbdaed25d19cc4
Suggested-by: Keith Busch kbusch@kernel.org Reported-and-tested-by: Jiwei Sun sunjw10@lenovo.com Signed-off-by: Adrian Huang ahuang12@lenovo.com Reviewed-by: Keith Busch kbusch@kernel.org Signed-off-by: Christoph Hellwig hch@lst.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/nvme/host/pci.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c index a7772c0194d5a..a389f1ea0b151 100644 --- a/drivers/nvme/host/pci.c +++ b/drivers/nvme/host/pci.c @@ -2960,7 +2960,7 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev, * over a single page. */ dev->ctrl.max_hw_sectors = min_t(u32, - NVME_MAX_KB_SZ << 1, dma_max_mapping_size(&pdev->dev) >> 9); + NVME_MAX_KB_SZ << 1, dma_opt_mapping_size(&pdev->dev) >> 9); dev->ctrl.max_segments = NVME_MAX_SEGS;
/*