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init: s/common_cpu/cpu_number

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related issue: #682

Thanks @PinoTsao

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
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Alexander Kuleshov 2022-07-31 16:01:52 +06:00
parent 24f50f0c00
commit 3920ef412a
1 changed files with 6 additions and 6 deletions
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12
Initialization/linux-initialization-4.md
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@ -266,13 +266,13 @@ Remember that we have passed `cpu_number` as `pcp` to the `this_cpu_read` from t
})
```
Yes, it looks a little strange but it's easy. First of all we can see the definition of the `pscr_ret__` variable with the `int` type. Why int? Ok, `variable` is `common_cpu` and it was declared as per-cpu int variable:
Yes, it looks a little strange but it's easy. First of all we can see the definition of the `pscr_ret__` variable with the `int` type. Why int? Ok, `variable` is `cpu_number` and it was declared as per-cpu int variable:
```C
DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);
```
In the next step we call `__verify_pcpu_ptr` with the address of `cpu_number`. `__veryf_pcpu_ptr` used to verify that the given parameter is a per-cpu pointer. After that we set `pscr_ret__` value which depends on the size of the variable. Our `common_cpu` variable is `int`, so it's 4 bytes in size. It means that we will get `this_cpu_read_4(common_cpu)` in `pscr_ret__`. In the end of the `__pcpu_size_call_return` we just call it. `this_cpu_read_4` is a macro:
In the next step we call `__verify_pcpu_ptr` with the address of `cpu_number`. `__veryf_pcpu_ptr` used to verify that the given parameter is a per-cpu pointer. After that we set `pscr_ret__` value which depends on the size of the variable. Our `cpu_number` variable is `int`, so it's 4 bytes in size. It means that we will get `this_cpu_read_4(cpu_number)` in `pscr_ret__`. In the end of the `__pcpu_size_call_return` we just call it. `this_cpu_read_4` is a macro:
```C
#define this_cpu_read_4(pcp) percpu_from_op("mov", pcp)
@ -281,19 +281,19 @@ In the next step we call `__verify_pcpu_ptr` with the address of `cpu_number`. `
which calls `percpu_from_op` and pass `mov` instruction and per-cpu variable there. `percpu_from_op` will expand to the inline assembly call:
```C
asm("movl %%gs:%1,%0" : "=r" (pfo_ret__) : "m" (common_cpu))
asm("movl %%gs:%1,%0" : "=r" (pfo_ret__) : "m" (cpu_number))
```
Let's try to understand how it works and what it does. The `gs` segment register contains the base of per-cpu area. Here we just copy `common_cpu` which is in memory to the `pfo_ret__` with the `movl` instruction. Or with another words:
Let's try to understand how it works and what it does. The `gs` segment register contains the base of per-cpu area. Here we just copy `cpu_number` which is in memory to the `pfo_ret__` with the `movl` instruction. Or with another words:
```C
this_cpu_read(common_cpu)
this_cpu_read(cpu_number)
```
is the same as:
```C
movl %gs:$common_cpu, $pfo_ret__
movl %gs:$cpu_number, $pfo_ret__
```
As we didn't setup per-cpu area, we have only one - for the current running CPU, we will get `zero` as a result of the `smp_processor_id`.