度量kernel各个部分的具体开销。
- lock cpu freq
cat /proc/cpuinfo | grep MHz
我测的10次
- syscall：14132最差，平均920上下
- page fault：1830、1352 都是100多
- 读写mov指令：都是30多，但是1000多mov也是30多，2000多最快是56，4096是108
- miss(_mm_clflush) 可能是mov的最少两倍，64cycles，最差1248cycles
Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference 0.5 ns
Branch mispredict 5 ns
L2 cache reference 7 ns 14x L1 cache
Mutex lock/unlock 25 ns
Main memory reference 100 ns 20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy 3,000 ns 3 us
Send 1K bytes over 1 Gbps network 10,000 ns 10 us
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD
Read 1 MB sequentially from memory 250,000 ns 250 us
Round trip within same datacenter 500,000 ns 500 us
Read 1 MB sequentially from SSD* 1,000,000 ns 1,000 us 1 ms ~1GB/sec SSD, 4X memory
Disk seek 10,000,000 ns 10,000 us 10 ms 20x datacenter roundtrip
Read 1 MB sequentially from disk 20,000,000 ns 20,000 us 20 ms 80x memory, 20X SSD
Send packet CA->Netherlands->CA 150,000,000 ns 150,000 us 150 ms
Notes
-----
1 ns = 10^-9 seconds
1 us = 10^-6 seconds = 1,000 ns
1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns
Credit
------
By Jeff Dean: http://research.google.com/people/jeff/
Originally by Peter Norvig: http://norvig.com/21-days.html#answers
Contributions
-------------
'Humanized' comparison: https://gist.github.com/hellerbarde/2843375
Visual comparison chart: http://i.imgur.com/k0t1e.png
- ubuntu21.10 里面装4.19.229内核的问题
initramfs failed to compress， junk files archive
主要原因是kernel4.x 不支持zstd压缩，但是ubuntu用zstd压缩了initramfs。
解决办法是在/etc/initramfs-tools/update-initramfs.conf里面把压缩算法改成支持的，比如gzip
- 小窍门
LOCALVERSION=-custom
make CC=clang -j8 LOCALVERSION=-custom 之后能够在kernel中显示自己命名的kernel version，比较好。