zsmalloc performance on ARM64 platform

To use zram the Linux kernel zsmalloc needs to be enabled. The zsmalloc functionality in turn allows to use two methods to access allocations of multiple pages: Copy-based or using VM mapping. Depending on platform one or the other is faster, and the configuration option already suggests that ARM the VM mapping method is typically faster. Hence I was wondering whether that is also true for ARM64 platforms (running in Aarch64 mode). Outcome: On a quad Cortex-A35 platform using Linux 4.14 VM mapping was ~20-50% faster.

The measurement was done using the zsmalloc microbenchmark linked in the kernel configuraiton. To work with Linux 4.14 I used this fork of zsmalloc. Here are the logs of two runs:

CONFIG_PGTABLE_MAPPING disabled

# insmod /tmp/zsmapbench.ko single_threaded=0
[ 70.243246] zsmapbench: loading out-of-tree module taints kernel.
[ 70.249970] running zsmapbench...
[ 70.253870] starting zsmb_kthread
[ 70.257112] starting zsmb_kthread
[ 70.257126] starting zsmb_kthread
[ 70.257132] starting zsmb_kthread
[ 71.269098] 8087556 cycles
[ 71.271911] 872547 mappings
[ 71.275308] 9 cycles/map
[ 71.278077] stopping zsmb_kthread
[ 71.281731] 8193562 cycles
[ 71.284443] 880742 mappings
[ 71.287268] 9 cycles/map
[ 71.289821] stopping zsmb_kthread
[ 71.293250] 8285606 cycles
[ 71.295963] 893724 mappings
[ 71.298778] 9 cycles/map
[ 71.301343] stopping zsmb_kthread
[ 71.304743] 8299217 cycles
[ 71.307469] 898431 mappings
[ 71.310296] 9 cycles/map
[ 71.312834] stopping zsmb_kthread
[ 71.316475] zsmapbench complete
...
# insmod /tmp/zsmapbench.ko single_threaded=1
[ 87.134504] running zsmapbench...
[ 87.138006] starting zsmb_kthread
[ 88.165339] 8189148 cycles
[ 88.168070] 1081365 mappings
[ 88.170984] 7 cycles/map
[ 88.173546] stopping zsmb_kthread
[ 88.177124] zsmapbench complete

CONFIG_PGTABLE_MAPPING enabled

# insmod /tmp/zsmapbench.ko single_threaded=0
[ 51.344365] zsmapbench: loading out-of-tree module taints kernel.
[ 51.351160] running zsmapbench...
[ 51.354916] starting zsmb_kthread
[ 51.354918] starting zsmb_kthread
[ 51.354967] starting zsmb_kthread
[ 51.357148] starting zsmb_kthread
[ 52.383034] 8196954 cycles
[ 52.385753] 721562 mappings
[ 52.388960] 11 cycles/map
[ 52.391766] stopping zsmb_kthread
[ 52.395384] 8215377 cycles
[ 52.398095] 720467 mappings
[ 52.400908] 11 cycles/map
[ 52.403545] stopping zsmb_kthread
[ 52.406945] 8413254 cycles
[ 52.409672] 738590 mappings
[ 52.412490] 11 cycles/map
[ 52.415133] stopping zsmb_kthread
[ 52.418524] 8489886 cycles
[ 52.421253] 744137 mappings
[ 52.424075] 11 cycles/map
[ 52.426703] stopping zsmb_kthread
[ 52.430352] zsmapbench complete
# insmod /tmp/zsmapbench.ko single_threaded=1
[ 67.197377] running zsmapbench...
[ 67.200880] starting zsmb_kthread
[ 68.223545] 8151926 cycles
[ 68.226268] 718261 mappings
[ 68.229083] 11 cycles/map
[ 68.231728] stopping zsmb_kthread
[ 68.235331] zsmapbench complete

 

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