Re: [Qemu-devel] [PATCH 4/10] Add dirty tracking for live migration

["Glauber Costa" <glommer@gmail.com>]

On Wed, Sep 10, 2008 at 11:56 AM, Anthony Liguori <anthony@codemonkey.ws> wrote:
> Glauber Costa wrote:
>>
>> On Tue, Sep 9, 2008 at 4:49 PM, Anthony Liguori <aliguori@us.ibm.com>
>> wrote:
>>
>>>
>>> This patch adds a dirty tracking bit for live migration.  We use 0x08
>>> because
>>> kqemu uses 0x04.
>>>
>>
>> For which purpose, and where is it? I think it deserves at least a
>> comment on the source itself for future generations.
>>
>
> This patch was originally written before kqemu was Open Sourced.  I only
> knew that kqemu used 0x08 because Fabrice mentioned it in reviewing the
> earliest version of this series.
>
> I'll add a comment to the code.
>
>>> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>>>
>>> diff --git a/cpu-all.h b/cpu-all.h
>>> index d350b30..fdac353 100644
>>> --- a/cpu-all.h
>>> +++ b/cpu-all.h
>>> @@ -944,6 +944,7 @@ int cpu_memory_rw_debug(CPUState *env, target_ulong
>>> addr,
>>>
>>>  #define VGA_DIRTY_FLAG  0x01
>>>  #define CODE_DIRTY_FLAG 0x02
>>> +#define MIGRATION_DIRTY_FLAG 0x08
>>>
>>>  /* read dirty bit (return 0 or 1) */
>>>  static inline int cpu_physical_memory_is_dirty(ram_addr_t addr)
>>> @@ -966,6 +967,10 @@ void cpu_physical_memory_reset_dirty(ram_addr_t
>>> start, ram_addr_t end,
>>>                                     int dirty_flags);
>>>  void cpu_tlb_update_dirty(CPUState *env);
>>>
>>> +int cpu_physical_memory_set_dirty_tracking(int enable);
>>> +
>>> +int cpu_physical_memory_get_dirty_tracking(void);
>>> +
>>>  void dump_exec_info(FILE *f,
>>>                    int (*cpu_fprintf)(FILE *f, const char *fmt, ...));
>>>
>>> diff --git a/exec.c b/exec.c
>>> index 3ab4ad0..9dba5c8 100644
>>> --- a/exec.c
>>> +++ b/exec.c
>>> @@ -38,6 +38,7 @@
>>>  #include "qemu-common.h"
>>>  #include "tcg.h"
>>>  #include "hw/hw.h"
>>> +#include "osdep.h"
>>>  #if defined(CONFIG_USER_ONLY)
>>>  #include <qemu.h>
>>>  #endif
>>> @@ -113,6 +114,7 @@ ram_addr_t phys_ram_size;
>>>  int phys_ram_fd;
>>>  uint8_t *phys_ram_base;
>>>  uint8_t *phys_ram_dirty;
>>> +static int in_migration;
>>>  static ram_addr_t phys_ram_alloc_offset = 0;
>>>  #endif
>>>
>>> @@ -1777,6 +1779,17 @@ void cpu_physical_memory_reset_dirty(ram_addr_t
>>> start, ram_addr_t end,
>>>    }
>>>  }
>>>
>>> +int cpu_physical_memory_set_dirty_tracking(int enable)
>>> +{
>>> +    in_migration = enable;
>>> +    return 0;
>>> +}
>>> +
>>> +int cpu_physical_memory_get_dirty_tracking(void)
>>> +{
>>> +    return in_migration;
>>> +}
>>> +
>>>  static inline void tlb_update_dirty(CPUTLBEntry *tlb_entry)
>>>  {
>>>    ram_addr_t ram_addr;
>>> @@ -2932,9 +2945,19 @@ void stl_phys_notdirty(target_phys_addr_t addr,
>>> uint32_t val)
>>>        io_index = (pd >> IO_MEM_SHIFT) & (IO_MEM_NB_ENTRIES - 1);
>>>        io_mem_write[io_index][2](io_mem_opaque[io_index], addr, val);
>>>    } else {
>>> -        ptr = phys_ram_base + (pd & TARGET_PAGE_MASK) +
>>> -            (addr & ~TARGET_PAGE_MASK);
>>> +        unsigned long addr1 = (pd & TARGET_PAGE_MASK) + (addr &
>>> ~TARGET_PAGE_MASK);
>>> +        ptr = phys_ram_base + addr1;
>>>        stl_p(ptr, val);
>>> +
>>> +        if (unlikely(in_migration)) {
>>> +            if (!cpu_physical_memory_is_dirty(addr1)) {
>>> +                /* invalidate code */
>>> +                tb_invalidate_phys_page_range(addr1, addr1 + 4, 0);
>>> +                /* set dirty bit */
>>> +                phys_ram_dirty[addr1 >> TARGET_PAGE_BITS] |=
>>> +                    (0xff & ~CODE_DIRTY_FLAG);
>>> +            }
>>> +        }
>>>    }
>>>  }
>>>
>>
>> did you mean MIGRATION_DIRTY_FLAG?
>>
>
> No.  We want to set all of the dirty bits except for the CODE_DIRTY_FLAG.
>  If you look around the rest of the code, it's pretty much the standard
> thing to do.  Self-modifying code has to be handled specially.

oh, you're right.

my bad.

> Regards,
>
> Anthony Liguori
>
>
>



-- 
Glauber Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."