On 12/6/18 9:49 PM, Dongli Zhang wrote: > > > On 12/07/2018 12:12 AM, Joe Jin wrote: >> Hi Dongli, >> >> Maybe move d_swiotlb_usage declare into swiotlb_create_debugfs(): > > I assume the call of swiotlb_tbl_map_single() might be frequent in some > situations, e.g., when 'swiotlb=force'. > > That's why I declare the d_swiotlb_usage out of any functions and use "if > (unlikely(!d_swiotlb_usage))".
This is reasonable. Thanks, Joe > > I think "if (unlikely(!d_swiotlb_usage))" incur less performance overhead than > calling swiotlb_create_debugfs() every time to confirm if debugfs is created. > I > would declare d_swiotlb_usage statically inside swiotlb_create_debugfs() if > the > performance overhead is acceptable (it is trivial indeed). > > > That is the reason I tag the patch with RFC because I am not sure if the > on-demand creation of debugfs is fine with maintainers/reviewers. If swiotlb > pages are never allocated, we would not be able to see the debugfs entry. > > I would prefer to limit the modification within swiotlb and to not taint any > other files. > > The drawback is there is no place to create or delete the debugfs entry > because > swiotlb buffer could be initialized and uninitialized at very early stage. > >> >> void swiotlb_create_debugfs(void) >> { >> #ifdef CONFIG_DEBUG_FS >> static struct dentry *d_swiotlb_usage = NULL; >> >> if (d_swiotlb_usage) >> return; >> >> d_swiotlb_usage = debugfs_create_dir("swiotlb", NULL); >> >> if (!d_swiotlb_usage) >> return; >> >> debugfs_create_file("usage", 0600, d_swiotlb_usage, >> NULL, &swiotlb_usage_fops); >> #endif >> } >> >> And for io_tlb_used, possible add a check at the begin of >> swiotlb_tbl_map_single(), >> if there were not any free slots or not enough slots, return fail directly? > > This would optimize the slots allocation path. I will follow this in next > version after I got more suggestions and confirmations from maintainers. > > > Thank you very much! > > Dongli Zhang > >> >> Thanks, >> Joe >> On 12/5/18 7:59 PM, Dongli Zhang wrote: >>> The device driver will not be able to do dma operations once swiotlb buffer >>> is full, either because the driver is using so many IO TLB blocks inflight, >>> or because there is memory leak issue in device driver. To export the >>> swiotlb buffer usage via debugfs would help the user estimate the size of >>> swiotlb buffer to pre-allocate or analyze device driver memory leak issue. >>> >>> As the swiotlb can be initialized at very early stage when debugfs cannot >>> register successfully, this patch creates the debugfs entry on demand. >>> >>> Signed-off-by: Dongli Zhang <dongli.zh...@oracle.com> >>> --- >>> kernel/dma/swiotlb.c | 57 >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 57 insertions(+) >>> >>> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c >>> index 045930e..d3c8aa4 100644 >>> --- a/kernel/dma/swiotlb.c >>> +++ b/kernel/dma/swiotlb.c >>> @@ -35,6 +35,9 @@ >>> #include <linux/scatterlist.h> >>> #include <linux/mem_encrypt.h> >>> #include <linux/set_memory.h> >>> +#ifdef CONFIG_DEBUG_FS >>> +#include <linux/debugfs.h> >>> +#endif >>> >>> #include <asm/io.h> >>> #include <asm/dma.h> >>> @@ -73,6 +76,13 @@ static phys_addr_t io_tlb_start, io_tlb_end; >>> */ >>> static unsigned long io_tlb_nslabs; >>> >>> +#ifdef CONFIG_DEBUG_FS >>> +/* >>> + * The number of used IO TLB block >>> + */ >>> +static unsigned long io_tlb_used; >>> +#endif >>> + >>> /* >>> * This is a free list describing the number of free entries available from >>> * each index >>> @@ -100,6 +110,41 @@ static DEFINE_SPINLOCK(io_tlb_lock); >>> >>> static int late_alloc; >>> >>> +#ifdef CONFIG_DEBUG_FS >>> + >>> +static struct dentry *d_swiotlb_usage; >>> + >>> +static int swiotlb_usage_show(struct seq_file *m, void *v) >>> +{ >>> + seq_printf(m, "%lu\n%lu\n", io_tlb_used, io_tlb_nslabs); >>> + return 0; >>> +} >>> + >>> +static int swiotlb_usage_open(struct inode *inode, struct file *filp) >>> +{ >>> + return single_open(filp, swiotlb_usage_show, NULL); >>> +} >>> + >>> +static const struct file_operations swiotlb_usage_fops = { >>> + .open = swiotlb_usage_open, >>> + .read = seq_read, >>> + .llseek = seq_lseek, >>> + .release = single_release, >>> +}; >>> + >>> +void swiotlb_create_debugfs(void) >>> +{ >>> + d_swiotlb_usage = debugfs_create_dir("swiotlb", NULL); >>> + >>> + if (!d_swiotlb_usage) >>> + return; >>> + >>> + debugfs_create_file("usage", 0600, d_swiotlb_usage, >>> + NULL, &swiotlb_usage_fops); >>> +} >>> + >>> +#endif >>> + >>> static int __init >>> setup_io_tlb_npages(char *str) >>> { >>> @@ -449,6 +494,11 @@ phys_addr_t swiotlb_tbl_map_single(struct device >>> *hwdev, >>> pr_warn_once("%s is active and system is using DMA bounce >>> buffers\n", >>> sme_active() ? "SME" : "SEV"); >>> >>> +#ifdef CONFIG_DEBUG_FS >>> + if (unlikely(!d_swiotlb_usage)) >>> + swiotlb_create_debugfs(); >>> +#endif >>> + >>> mask = dma_get_seg_boundary(hwdev); >>> >>> tbl_dma_addr &= mask; >>> @@ -528,6 +578,9 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, >>> dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", >>> size); >>> return SWIOTLB_MAP_ERROR; >>> found: >>> +#ifdef CONFIG_DEBUG_FS >>> + io_tlb_used += nslots; >>> +#endif >>> spin_unlock_irqrestore(&io_tlb_lock, flags); >>> >>> /* >>> @@ -588,6 +641,10 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, >>> phys_addr_t tlb_addr, >>> */ >>> for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != >>> IO_TLB_SEGSIZE -1) && io_tlb_list[i]; i--) >>> io_tlb_list[i] = ++count; >>> + >>> +#ifdef CONFIG_DEBUG_FS >>> + io_tlb_used -= nslots; >>> +#endif >>> } >>> spin_unlock_irqrestore(&io_tlb_lock, flags); >>> } >>> >> >> _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu