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Shaohua Li authored
I'm testing swapout workload in a two-socket Xeon machine. The workload has 10 threads, each thread sequentially accesses separate memory region. TLB flush overhead is very big in the workload. For each page, page reclaim need move it from active lru list and then unmap it. Both need a TLB flush. And this is a multthread workload, TLB flush happens in 10 CPUs. In X86, TLB flush uses generic smp_call)function. So this workload stress smp_call_function_many heavily. Without patch, perf shows: + 24.49% [k] generic_smp_call_function_interrupt - 21.72% [k] _raw_spin_lock - _raw_spin_lock + 79.80% __page_check_address + 6.42% generic_smp_call_function_interrupt + 3.31% get_swap_page + 2.37% free_pcppages_bulk + 1.75% handle_pte_fault + 1.54% put_super + 1.41% grab_super_passive + 1.36% __swap_duplicate + 0.68% blk_flush_plug_list + 0.62% swap_info_get + 6.55% [k] flush_tlb_func + 6.46% [k] smp_call_function_many + 5.09% [k] call_function_interrupt + 4.75% [k] default_send_IPI_mask_sequence_phys + 2.18% [k] find_next_bit swapout throughput is around 1300M/s. With the patch, perf shows: - 27.23% [k] _raw_spin_lock - _raw_spin_lock + 80.53% __page_check_address + 8.39% generic_smp_call_function_single_interrupt + 2.44% get_swap_page + 1.76% free_pcppages_bulk + 1.40% handle_pte_fault + 1.15% __swap_duplicate + 1.05% put_super + 0.98% grab_super_passive + 0.86% blk_flush_plug_list + 0.57% swap_info_get + 8.25% [k] default_send_IPI_mask_sequence_phys + 7.55% [k] call_function_interrupt + 7.47% [k] smp_call_function_many + 7.25% [k] flush_tlb_func + 3.81% [k] _raw_spin_lock_irqsave + 3.78% [k] generic_smp_call_function_single_interrupt swapout throughput is around 1400M/s. So there is around a 7% improvement, and total cpu utilization doesn't change. Without the patch, cfd_data is shared by all CPUs. generic_smp_call_function_interrupt does read/write cfd_data several times which will create a lot of cache ping-pong. With the patch, the data becomes per-cpu. The ping-pong is avoided. And from the perf data, this doesn't make call_single_queue lock contend. Next step is to remove generic_smp_call_function_interrupt() from arch code. Signed-off-by:
Shaohua Li <shli@fusionio.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Ingo Molnar <mingo@elte.hu> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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