测试sd卡的读写速度
mmc驱动测速
结合mmc子系统提供的测试列表进行速度测试和其他相关测试。
添加配置
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| ->DeviceDriver
-> MMC/SD/SDIO card support (MMC [=y])
[*]MMC host test driver
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绑定
编译并启动新编译的linux内核，进入文件系统。
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| cd sys/bus/mmc/drivers/mmcblk
echo mmc0:e624 > unbind
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| cd sys/bus/mmc/drivers/mmc_test
echo mmc0:e624 > bind
[ 17.243808] mmc_test mmc0:e624: Card claimed for testing.
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挂载debugfs
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| # mount -t debugfs none /mnt
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测试
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| #cat testlist
1: Basic write (no data verification)
2: Basic read (no data verification)
3: Basic write (with data verification)
4: Basic read (with data verification)
5: Multi-block write
6: Multi-block read
7: Power of two block writes
8: Power of two block reads
9: Weird sized block writes
10: Weird sized block reads
11: Badly aligned write
12: Badly aligned read
13: Badly aligned multi-block write
14: Badly aligned multi-block read
15: Correct xfer_size at write (start failure)
16: Correct xfer_size at read (start failure)
17: Correct xfer_size at write (midway failure)
18: Correct xfer_size at read (midway failure)
19: Highmem write
20: Highmem read
21: Multi-block highmem write
22: Multi-block highmem read
23: Best-case read performance
24: Best-case write performance
25: Best-case read performance into scattered pages
26: Best-case write performance from scattered pages
27: Single read performance by transfer size
28: Single write performance by transfer size
29: Single trim performance by transfer size
30: Consecutive read performance by transfer size
31: Consecutive write performance by transfer size
32: Consecutive trim performance by transfer size
33: Random read performance by transfer size
34: Random write performance by transfer size
35: Large sequential read into scattered pages
36: Large sequential write from scattered pages
37: Write performance with blocking req 4k to 4MB
38: Write performance with non-blocking req 4k to 4MB
39: Read performance with blocking req 4k to 4MB
40: Read performance with non-blocking req 4k to 4MB
41: Write performance blocking req 1 to 512 sg elems
42: Write performance non-blocking req 1 to 512 sg elems
43: Read performance blocking req 1 to 512 sg elems
44: Read performance non-blocking req 1 to 512 sg elems
45: eMMC hardware reset
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测试命令 dd
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| dd if=/dev/zero of=/dev/null
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dd if=[STDIN] of=[STDOUT]
bs: dd -ibs=[BYTE] -obs=[SIZE]
bs=BYTES
seek=BLOCKS
skip=BLOCKS
写测试
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| dd if=/dev/zero of=/mnt/sd/test.txt bs=512 count=100
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写数据量：512*100 / 1024 = 50Kb
读测试
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| dd if=/mnt/sd/test.txt of=/dev/null bs=512 count=100
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读数据量：512*100 / 1024 = 50Kb
PC测试
在pc上使用以上命令，将读写的目标改为（/dev/sdb）即可得到当前的读写速度
开发板测试
由于在开发板中的文件系统使用busybox编译生成，其中的dd命令无法直接得到读写速度，因此需要结合time命令
写测试
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| time dd if=/dev/zero of=/mnt/sd/test.txt bs=512 count=100
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写数据量：512*100 / 1024 = 50Kb
读测试
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| time dd if=/mnt/sd/test.txt of=/dev/null bs=512 count=100
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读数据量：512*100 / 1024 = 50Kb
注意事项
- 在对sd进行测速时，使用以上命令进行读写操作，文件系统会将该数据块进行一定大小（128个block为一个单元，即一个request请求）的分割，并将其传入sd驱动。在mmc驱动中配置msc控制器的block count大小时，其值为VFS层传入的128blk。
也就是说一个大于128个block数据块的读写，在mmc驱动中使用若干个request请求进行读写操作完成。
- 写测试增加conv=fsync参数
该参数可通过dd -h查看，作用将写的数据完全写入到sd完成返回，但是使用后根据写操作所得到的时间计算的写速度将降低
主要原因是，使用fsync后文件系统会将写的数据块根据bs的大小进行分割，也就是将其分割成count个bs。如果bs为512时，一次request请求的block count为512，加大了request请求次数，同时将增加sd驱动中的中断次数和读及等状态的次数，继而增大了写操作的时间，最后计算的写速度将降低。
总结
读写速率和以下情况有关：
- 外部通信时钟；
- DDR时钟，
- 代码运行速率，和CPU时钟、L2CACHE时钟有关
- 当前系统负荷
- 内部的总线时钟，比如MMC控制器所在的APB总线等
- MMC控制器的DMA工作时钟
- 读写代码的流程
- MSC的通信数据线的位数
- 读写的位置是否连续。
其中瓶颈是在（1）SD的通信速率（7）代码的流程（8）SD卡通信所占用的数据线（9）读写的位置是否连续