I've been very remiss in posting benchmarks; this isn't much, but if
anyone has suggestions for what they want I'll see if I can run it.
This is on an old corsair nova - bcache can go something like 10x faster
but this is what I have at home. The profile is still interesting,
though.
The benchmark is 4k random O_DIRECT reads on a 16 gb file, all in cache
- the idea is to push the b+tree.
Also, the backing device is a md raid10 - so that's working, provided
you format your cache with buckets not greater than 1 mb.
root@utumno:/mnt# perf record -afg fio ~/rw4k
randwrite: (g=0): rw=randread, bs=4K-4K/4K-4K, ioengine=libaio, iodepth=64
fio 1.59
Starting 1 process
Jobs: 1 (f=1): [r] [100.0% done] [69914K/0K /s] [17.7K/0 iops] [eta 00m:00s]
randwrite: (groupid=0, jobs=1): err= 0: pid=1247
read : io=16384MB, bw=68713KB/s, iops=17178 , runt=244169msec
cpu : usr=5.66%, sys=22.93%, ctx=4198688, majf=0, minf=85
IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >=64=100.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.1%, >=64=0.0%
issued r/w/d: total=4194367/0/0, short=0/0/0
Run status group 0 (all jobs):
READ: io=16384MB, aggrb=68712KB/s, minb=70361KB/s, maxb=70361KB/s, mint=244169msec, maxt=244169msec
Disk stats (read/write):
bcache0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%
7.74% fio fio [.] 0x1d2ed
5.26% swapper [kernel.kallsyms] [k] ahci_interrupt
3.02% swapper [kernel.kallsyms] [k] mwait_idle
2.52% swapper [kernel.kallsyms] [k] _raw_spin_lock_irqsave
1.82% swapper [kernel.kallsyms] [k] ahci_scr_read
1.68% fio [kernel.kallsyms] [k] __bset_search <- first bcache function
1.37% fio [kernel.kallsyms] [k] __blockdev_direct_IO
1.36% swapper [kernel.kallsyms] [k] irq_entries_start
1.25% swapper [kernel.kallsyms] [k] mix_pool_bytes_extract
1.06% swapper [kernel.kallsyms] [k] kmem_cache_free
0.94% fio [kernel.kallsyms] [k] __switch_to
0.92% fio [kernel.kallsyms] [k] system_call
0.87% swapper [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
0.84% swapper [kernel.kallsyms] [k] ata_qc_new_init
0.80% fio [kernel.kallsyms] [k] __schedule
0.76% fio [kernel.kallsyms] [k] do_io_submit
0.74% fio [kernel.kallsyms] [k] _raw_spin_lock_irq
0.74% swapper [kernel.kallsyms] [k] _raw_spin_lock
0.73% fio [kernel.kallsyms] [k] ext4_ext_find_extent
0.71% fio [kernel.kallsyms] [k] kmem_cache_alloc
0.70% fio [kernel.kallsyms] [k] read_events
0.65% fio libaio.so.1.0.1 [.] 0x665
0.64% swapper [kernel.kallsyms] [k] __schedule
0.63% swapper [kernel.kallsyms] [k] native_sched_clock
0.63% fio [kernel.kallsyms] [k] btree_search_leaf <- second bcache function
0.62% fio [kernel.kallsyms] [k] bcache_make_request
0.59% swapper [kernel.kallsyms] [k] read_tsc
0.58% fio [kernel.kallsyms] [k] aio_read_evt
0.58% swapper [kernel.kallsyms] [k] select_task_rq_fair
0.57% swapper [kernel.kallsyms] [k] tick_nohz_stop_sched_tick
0.57% fio [kernel.kallsyms] [k] __request_read
0.57% fio [kernel.kallsyms] [k] generic_make_request
0.56% swapper [kernel.kallsyms] [k] sd_prep_fn
0.53% fio [kernel.kallsyms] [k] _raw_spin_lock
0.51% swapper [kernel.kallsyms] [k] __hrtimer_start_range_ns
0.50% fio [kernel.kallsyms] [k] __math_state_restore
Some of the calls to kmem_cache_(free|alloc) are of course from bcache
but it looks to be under 25%.
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