Hi Robin, On 12/07/2018 09:17 PM, Robin Murphy wrote: > On 07/12/2018 05:49, 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))". >> >> 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. > > Couldn't you just do it from an initcall? All you really need to care about is > ordering after debugfs_init(), which is easy. If SWIOTLB initialisation does > end > up being skipped at any point, nobody's going to mind if debugfs still has an > entry saying io_tlb_nslabs == 0 (in fact, that's arguably useful in itself as > positive confirmation that the system is not using SWIOTLB).
I will put the creation of debugfs entry in late_initcall() which is the last initcall. > >>> 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); > > Maybe expose io_tlb_nslabs and io_tlb_used as separate entries? Then you could > just use debugfs_create_ulong() to keep things really simple. That would also > make the interface more consistent with dma-debug, which would be nice given > how > closely-related they are. I will switch to debugfs_create_ulong() and that will also reduce the LOC. Thank you very much! Dongli Zhang > > Robin. > >>> #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, ); >>>> + 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