Networking drivers very often have to replace one page with another for their RX ring buffers.
A multi-queue NIC will severly hit a contention point in dma-debug while grabbing free_entries_lock spinlock. Adding a one entry per-cpu cache removes the need to grab this spinlock twice per page replacement. Tested on a 40Gbit mlx4 NIC, with 16 RX queues and about 1,000,000 replacements per second. Signed-off-by: Eric Dumazet <eduma...@google.com> Cc: Christoph Hellwig <h...@lst.de> --- kernel/dma/debug.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index a310dbb1515e92c081f8f3f9a7290dd5e53fc889..b7221426ef49cf640db5bcb261b0817d714a3033 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -97,6 +97,8 @@ static LIST_HEAD(free_entries); /* Lock for the list above */ static DEFINE_SPINLOCK(free_entries_lock); +static DEFINE_PER_CPU(struct dma_debug_entry *, dma_debug_entry_cache); + /* Global disable flag - will be set in case of an error */ static bool global_disable __read_mostly; @@ -676,6 +678,10 @@ static struct dma_debug_entry *dma_entry_alloc(void) struct dma_debug_entry *entry; unsigned long flags; + entry = this_cpu_xchg(dma_debug_entry_cache, NULL); + if (entry) + goto end; + spin_lock_irqsave(&free_entries_lock, flags); if (num_free_entries == 0) { if (dma_debug_create_entries(GFP_ATOMIC)) { @@ -690,7 +696,7 @@ static struct dma_debug_entry *dma_entry_alloc(void) entry = __dma_entry_alloc(); spin_unlock_irqrestore(&free_entries_lock, flags); - +end: #ifdef CONFIG_STACKTRACE entry->stack_len = stack_trace_save(entry->stack_entries, ARRAY_SIZE(entry->stack_entries), @@ -705,6 +711,9 @@ static void dma_entry_free(struct dma_debug_entry *entry) active_cacheline_remove(entry); + if (!this_cpu_cmpxchg(dma_debug_entry_cache, NULL, entry)) + return; + /* * add to beginning of the list - this way the entries are * more likely cache hot when they are reallocated. -- 2.25.0.341.g760bfbb309-goog _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu