Messages in this thread Patch in this message | | | From | Guo Hui <> | Subject | [PATCH] timekeeping:add padding in timekeeper for Unixbench pipe | Date | Fri, 6 Jan 2023 14:29:46 +0800 |
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When the LLC cache line size is 128 bytes, such as Kunpeng 920, the seq attribute and xtime attribute in the structure tk_core are completely in the same LLC cache line, and xtime_sec is the data protected by the seq lock in the function ktime_get_coarse_real_ts64, so seq and xtime_sec are in the same LLC cache line causing the false sharing problem.
Adding padding before xtime_sec in the structure timekeeper is based on the comment of the structure tk_read_base: "This struct has size 56 byte on 64 bit. Together with a seqcount it occupies a single 64byte cache line." Therefore, seq and the structure tk_read_base should be placed in the same 64-byte cacheline.
The performance data of Unixbench pipe on Kunpeng 920 is as follows:
Enable the LSE instruction: seq and xtime are in the same LLC cache line: System Benchmarks Partial Index BASELINE RESULT INDEX Pipe Throughput 12440.0 14800574.4 11897.6 Pipe-based Context Switching 4000.0 4357419.0 10893.5 ======== System Benchmarks Index Score (Partial Only) 11384.5
seq and xtime are not in the same LLC cache line: System Benchmarks Partial Index BASELINE RESULT INDEX Pipe Throughput 12440.0 16546306.6 13300.9 Pipe-based Context Switching 4000.0 5654281.8 14135.7 ======== System Benchmarks Index Score (Partial Only) 13711.9
When the LSE instruction is enabled, Pipe Throughput increases by 11.79%, and Pipe-based Context Switching increases by 29.76%.
Close the LSE instruction: seq and xtime are in the same LLC cache line: System Benchmarks Partial Index BASELINE RESULT INDEX Pipe Throughput 12440.0 36375286.5 29240.6 Pipe-based Context Switching 4000.0 11994739.7 29986.8 ======== System Benchmarks Index Score (Partial Only) 29611.4
seq and xtime are not in the same LLC cache line: System Benchmarks Partial Index BASELINE RESULT INDEX Pipe Throughput 12440.0 44887148.8 36082.9 Pipe-based Context Switching 4000.0 13666392.0 34166.0 ======== System Benchmarks Index Score (Partial Only) 35111.4
When the LSE instruction is disabled, Pipe Throughput increases by 23.40%, and Pipe-based Context Switching increases by 13.94%.
Signed-off-by: Guo Hui <guohui@uniontech.com> --- include/linux/timekeeper_internal.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index 84ff2844d..d363cd1f3 100644 --- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h @@ -92,6 +92,7 @@ struct tk_read_base { struct timekeeper { struct tk_read_base tkr_mono; struct tk_read_base tkr_raw; + u64 padding; u64 xtime_sec; unsigned long ktime_sec; struct timespec64 wall_to_monotonic; -- 2.20.1
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