Linux
如何實現 emmc 分區的最佳對齊？
我們有包含 eMMC 的基於 bbb 的定制板。
我們創建瞭如下分區，
parted --script -a minimal /dev/mmcblk0 \ mklabel gpt \ mkpart primary 131072B 262143B \ mkpart primary 262144B 393215B \ mkpart primary 393216B 524287B \ mkpart primary 524288B 1572863B \ mkpart primary 1572864B 2621439B \ mkpart primary 2621440B 3145727B \ mkpart primary 3145728B 3276799B \ mkpart primary 3276800B 8519679B \ mkpart primary 8519680B 13762559B \ mkpart primary 13762560B 19005439B \ mkpart primary 19005440B 19267583B \ mkpart primary 19267584B 19529727B \ mkpart primary 19529728B 19791871B \ mkpart primary 20MiB 31MiB \ mkpart primary ext4 32MiB 232MiB \ mkpart primary ext4 232MiB 432MiB \ mkpart primary ext4 432MiB 532MiB \ mkpart primary ext4 532MiB 592MiB \ mkpart primary ext4 592MiB 792MiB \ mkpart primary ext4 792MiB 827MiB \ mkpart primary ext4 827MiB 3650MiB \使用上述命令，我們可以對 eMMC 進行分區，但對齊設置為最小。我們想檢查如何實現最佳對齊？實現最佳對齊有什麼優勢嗎？我提到了這個連結，但
parted -a opt /dev/sdb mkpart primary 0% 100%不能使用像這樣的解決方案，因為我們需要以下結構。# parted --list Model: MMC MMC04G (sd/mmc) Disk /dev/mmcblk0: 3842MB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 131kB 262kB 131kB 2 262kB 393kB 131kB 3 393kB 524kB 131kB 4 524kB 1573kB 1049kB 5 1573kB 2621kB 1049kB 6 2621kB 3146kB 524kB 7 3146kB 3277kB 131kB 8 3277kB 8520kB 5243kB 9 8520kB 13.8MB 5243kB 10 13.8MB 19.0MB 5243kB 11 19.0MB 19.3MB 262kB 12 19.3MB 19.5MB 262kB 13 19.5MB 19.8MB 262kB 14 21.0MB 32.5MB 11.5MB 15 33.6MB 243MB 210MB ext4 16 243MB 453MB 210MB ext4 17 453MB 558MB 105MB ext4 18 558MB 621MB 62.9MB ext4 19 621MB 830MB 210MB ext4 20 830MB 867MB 36.7MB ext4 21 867MB 3827MB 2960MB ext4使用目前命令，如果我們替換
minimal為，optimal我們會看到來自 parted 的以下消息，Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance. Warning: The resulting partition is not properly aligned for best performance.任何指針/建議/更正以實現最佳對齊？
正如此連結中所建議的，我提取了以下值，
# cat /sys/class/mmc_host/mmc1/mmc1\:0001/block/mmcblk0/queue/optimal_io_size 0 # cat /sys/class/mmc_host/mmc1/mmc1\:0001/block/mmcblk0/queue/minimum_io_size 512 # cat /sys/class/mmc_host/mmc1/mmc1\:0001/block/mmcblk0/alignment_offset 0 # cat /sys/class/mmc_host/mmc1/mmc1\:0001/block/mmcblk0/queue/physical_block_siz e 512mmc utils 給出以下輸出，
# ./mmc extcsd read /dev/mmcblk0 ============================================= Extended CSD rev 1.5 (MMC 4.41) ============================================= Card Supported Command sets [S_CMD_SET: 0x01] HPI Features [HPI_FEATURE: 0x03]: implementation based on CMD12 Background operations support [BKOPS_SUPPORT: 0x01] Background operations status [BKOPS_STATUS: 0x02] 1st Initialisation Time after programmed sector [INI_TIMEOUT_AP: 0x7a] Power class for 52MHz, DDR at 3.6V [PWR_CL_DDR_52_360: 0x00] Power class for 52MHz, DDR at 1.95V [PWR_CL_DDR_52_195: 0x00] Minimum Performance for 8bit at 52MHz in DDR mode: [MIN_PERF_DDR_W_8_52: 0x00] [MIN_PERF_DDR_R_8_52: 0x00] TRIM Multiplier [TRIM_MULT: 0x06] Secure Feature support [SEC_FEATURE_SUPPORT: 0x15] Secure Erase Multiplier [SEC_ERASE_MULT: 0x02] Secure TRIM Multiplier [SEC_TRIM_MULT: 0x03] Boot Information [BOOT_INFO: 0x07] Device supports alternative boot method Device supports dual data rate during boot Device supports high speed timing during boot Boot partition size [BOOT_SIZE_MULTI: 0x10] Access size [ACC_SIZE: 0x06] High-capacity erase unit size [HC_ERASE_GRP_SIZE: 0x08] i.e. 4096 KiB High-capacity erase timeout [ERASE_TIMEOUT_MULT: 0x01] Reliable write sector count [REL_WR_SEC_C: 0x01] High-capacity W protect group size [HC_WP_GRP_SIZE: 0x01] i.e. 4096 KiB Sleep current (VCC) [S_C_VCC: 0x08] Sleep current (VCCQ) [S_C_VCCQ: 0x08] Sleep/awake timeout [S_A_TIMEOUT: 0x10] Sector Count [SEC_COUNT: 0x00728000] Device is block-addressed Minimum Write Performance for 8bit: [MIN_PERF_W_8_52: 0x08] [MIN_PERF_R_8_52: 0x08] [MIN_PERF_W_8_26_4_52: 0x08] [MIN_PERF_R_8_26_4_52: 0x08] Minimum Write Performance for 4bit: [MIN_PERF_W_4_26: 0x08] [MIN_PERF_R_4_26: 0x08] Power classes registers: [PWR_CL_26_360: 0x00] [PWR_CL_52_360: 0x00] [PWR_CL_26_195: 0x00] [PWR_CL_52_195: 0x00] Partition switching timing [PARTITION_SWITCH_TIME: 0x01] Out-of-interrupt busy timing [OUT_OF_INTERRUPT_TIME: 0x02] Card Type [CARD_TYPE: 0x07] HS Dual Data Rate eMMC @52MHz 1.8V or 3VI/O HS eMMC @52MHz - at rated device voltage(s) HS eMMC @26MHz - at rated device voltage(s) CSD structure version [CSD_STRUCTURE: 0x02] Command set [CMD_SET: 0x00] Command set revision [CMD_SET_REV: 0x00] Power class [POWER_CLASS: 0x00] High-speed interface timing [HS_TIMING: 0x01] Erased memory content [ERASED_MEM_CONT: 0x00] Boot configuration bytes [PARTITION_CONFIG: 0x00] Not boot enable No access to boot partition Boot config protection [BOOT_CONFIG_PROT: 0x00] Boot bus Conditions [BOOT_BUS_CONDITIONS: 0x00] High-density erase group definition [ERASE_GROUP_DEF: 0x01] Boot write protection status registers [BOOT_WP_STATUS]: 0x00 Boot Area Write protection [BOOT_WP]: 0x00 Power ro locking: possible Permanent ro locking: possible ro lock status: not locked User area write protection register [USER_WP]: 0x00 FW configuration [FW_CONFIG]: 0x00 RPMB Size [RPMB_SIZE_MULT]: 0x01 Write reliability setting register [WR_REL_SET]: 0x00 user area: existing data is at risk if a power failure occurs during a write operation partition 1: existing data is at risk if a power failure occurs during a write operation partition 2: existing data is at risk if a power failure occurs during a write operation partition 3: existing data is at risk if a power failure occurs during a write operation partition 4: existing data is at risk if a power failure occurs during a write operation Write reliability parameter register [WR_REL_PARAM]: 0x05 Device supports writing EXT_CSD_WR_REL_SET Device supports the enhanced def. of reliable write Enable background operations handshake [BKOPS_EN]: 0x00 H/W reset function [RST_N_FUNCTION]: 0x00 HPI management [HPI_MGMT]: 0x01 Partitioning Support [PARTITIONING_SUPPORT]: 0x03 Device support partitioning feature Device can have enhanced tech. Max Enhanced Area Size [MAX_ENH_SIZE_MULT]: 0x0001ca i.e. 1875968 KiB Partitions attribute [PARTITIONS_ATTRIBUTE]: 0x00 Partitioning Setting [PARTITION_SETTING_COMPLETED]: 0x00 Device partition setting NOT complete General Purpose Partition Size [GP_SIZE_MULT_4]: 0x000000 [GP_SIZE_MULT_3]: 0x000000 [GP_SIZE_MULT_2]: 0x000000 [GP_SIZE_MULT_1]: 0x000000 Enhanced User Data Area Size [ENH_SIZE_MULT]: 0x000000 i.e. 0 KiB Enhanced User Data Start Address [ENH_START_ADDR]: 0x000000 i.e. 0 bytes offset Bad Block Management mode [SEC_BAD_BLK_MGMNT]: 0x00編輯：按照“Глеб Майоров”的建議實現了最佳對齊，除了前 3 個分區（我無法更改），其他小分區更改為最小 1MiB 大小。並且除了 3 個分區，所有其他分區似乎都對齊了。這是我用於 eMMC 的最新分區腳本。（請注意：在下面的腳本中，我在上面的腳本中更改了分區大小）
parted --script -a optimal /dev/mmcblk0 \ mklabel gpt \ mkpart primary 128KiB 255KiB \ mkpart primary 256KiB 383KiB \ mkpart primary 384KiB 511KiB \ mkpart primary 1MiB 2MiB \ mkpart primary 2MiB 3MiB \ mkpart primary 3MiB 4MiB \ mkpart primary 4MiB 5MiB \ mkpart primary 5MiB 10MiB \ mkpart primary 10MiB 15MiB \ mkpart primary 15MiB 20MiB \ mkpart primary 20MiB 21MiB \ mkpart primary 21MiB 22MiB \ mkpart primary 22MiB 23MiB \ mkpart primary 23MiB 30MiB \ mkpart primary ext4 30MiB 530MiB \ mkpart primary ext4 530MiB 1030MiB \ mkpart primary ext4 1030MiB 1130MiB \ mkpart primary ext4 1130MiB 1190MiB \ mkpart primary ext4 1190MiB 1720MiB \ mkpart primary ext4 1720MiB 1755MiB \ mkpart primary ext4 1755MiB 100%
嘗試與 eMMC 擦除塊大小對齊。它通常等於 0.5、1、2、4、8 MiB，具體取決於 eMMC 數據表。如果你發現塊大小對齊過多的記憶體浪費，那麼堅持頁面大小，通常在 4..16 KiB 的範圍內。
嘗試使分區大小和邊界成為擦除塊大小的倍數，這樣當文件系統寫入第一個或最後一個 FS 塊時，儲存卡不必擦除和重寫下一個/上一個分區的開始/結束。
不要依賴
parted’s 的功能來對齊，只需拿一個計算器、筆和一張紙，然後以扇區或字節為單位計算一個正確的邊界。就個人而言，我更喜歡對齊到 8 MiB 邊框，因為它不會浪費太多記憶體，並且任何分區都在擦除塊邊框上開始和結束，無論具體擦除塊大小如何，所以我不需要搜尋儲存卡文件。
最佳對齊降低了寫入放大係數，因此您的記憶體可以持續更長時間。