On Thu, Jul 07, 2022 at 04:24:36AM -0400, Tianyu Lan wrote: > From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> > > Traditionally swiotlb was not performance critical because it was only > used for slow devices. But in some setups, like TDX/SEV confidential > guests, all IO has to go through swiotlb. Currently swiotlb only has a > single lock. Under high IO load with multiple CPUs this can lead to > significat lock contention on the swiotlb lock. > > This patch splits the swiotlb bounce buffer pool into individual areas > which have their own lock. Each CPU tries to allocate in its own area > first. Only if that fails does it search other areas. On freeing the > allocation is freed into the area where the memory was originally > allocated from. > > Area number can be set via swiotlb kernel parameter and is default > to be possible cpu number. If possible cpu number is not power of > 2, area number will be round up to the next power of 2. > > This idea from Andi Kleen patch(https://github.com/intel/tdx/commit/ > 4529b5784c141782c72ec9bd9a92df2b68cb7d45). Thanks, this looks much better. I think there is a small problem with how default_nareas is set - we need to use 0 as the default so that an explicit command line value of 1 works. Als have you checked the interaction with swiotlb_adjust_size in detail? diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 5536d2cd69d30..85b1c29dd0eb8 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -70,7 +70,7 @@ struct io_tlb_mem io_tlb_default_mem; phys_addr_t swiotlb_unencrypted_base; static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT; -static unsigned long default_nareas = 1; +static unsigned long default_nareas; /** * struct io_tlb_area - IO TLB memory area descriptor @@ -90,7 +90,10 @@ struct io_tlb_area { static void swiotlb_adjust_nareas(unsigned int nareas) { - if (!is_power_of_2(nareas)) + if (default_nareas) + return; + + if (nareas > 1 && !is_power_of_2(nareas)) nareas = roundup_pow_of_two(nareas); default_nareas = nareas; @@ -338,8 +341,7 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags, panic("%s: Failed to allocate %zu bytes align=0x%lx\n", __func__, alloc_size, PAGE_SIZE); - if (default_nareas == 1) - swiotlb_adjust_nareas(num_possible_cpus()); + swiotlb_adjust_nareas(num_possible_cpus()); mem->areas = memblock_alloc(sizeof(struct io_tlb_area) * default_nareas, SMP_CACHE_BYTES); @@ -410,8 +412,7 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask, (PAGE_SIZE << order) >> 20); } - if (default_nareas == 1) - swiotlb_adjust_nareas(num_possible_cpus()); + swiotlb_adjust_nareas(num_possible_cpus()); area_order = get_order(array_size(sizeof(*mem->areas), default_nareas));
