[Qemu-devel] I have a question about qemu’s li ve migration function.

Hello, mailing lists.

I have a question about qemu’s live migration function.

First, Let me introduce my source versions. I don’t know my Qemu’s version. Because I am using Kemari Projects newest version. And, my host kernel version is Linux kernel 3.6.0.

I want to know Qemu’s migration process.(Especially, arch_init.c ‘s ram_save_live function.)

Q1.

I am trying to know, brief algorythm’s process of my version. I paste my version’s code below of mail.

I guess, this process is occur.

1. Every time, this functions is called, We sync Qemu’s ram_list’s dirty bitmap to KVM’s. But, Null is returned at first time, because cpu_physical_memory_set_dirty_tracking(1); is not setted. In Second iteration’s, Qemu’s dirty bitmap is synchronized to KVM’s dirty bitmap.

2. In first call(after migration command is typed), cpu_physical_sync_dirty_bitmap doesn’t synchronized our qemu’s ram_list’s dirty bitmap. So, We must set all ram_list’s dirty bitmap to 1(Dirty).

3. Enable, KVM can return dirty bitmap. after this code, cpu_physical_sync_dirty_bitmap can work.

4. (Maybe) put metadata(not data) to Qemu file.

5. Another thread change stage to 2, and Iteratively copy dirty bytes.

6. Stage is shift to 3 and, Stop system to prevent dirty memory bit is generated. And, put system status to Qemu files.(Stop-And-Copy phase)

Is this right?

Q2.

I am trying to check my guess is right. But, my guess is not right. I want to know why.

Test 1.

If I disable 2(Set all block’s dirtybitmap to 0xFFFFFFFFUL), System transfer only dirty data and, Stop-And-Copy phase is going to very long time. So, I comment out this code.

#if 0

/* Make sure all dirty bits are set */

QLIST_FOREACH(block, &ram_list.blocks, next)

{

for (addr = block->offset; addr < block->offset + block->length;

addr += TARGET_PAGE_SIZE)

{

if (!cpu_physical_memory_get_dirty(addr,MIGRATION_DIRTY_FLAG))

{

cpu_physical_memory_set_dirty(addr);

//printf("addr is %lu",addr);

}

#endif

result1.

remaining data is going bigger.

Test2.

If I reset dirty bitmap before stage2’s put code, I can check stage2’s data transfer rate to very small. So I insert next code in stage2.(line 315 of below code.) I insert first_trans flag, to execute this code one time.

//Make sure stage2's first iteration doesn't send anything.

if(stage == 2 && first_trans)

{

RAMBlock *block;

first_trans=0;

QLIST_FOREACH(block, &ram_list.blocks, next)

{

for (addr = block->offset; addr < block->offset + block->length;

addr += TARGET_PAGE_SIZE)

{

if (!cpu_physical_memory_get_dirty(addr,MIGRATION_DIRTY_FLAG))

{

//cpu_physical_memory_set_dirty(addr);

cpu_physical_memory_reset_dirty(addr, addr+TARGET_PAGE_SIZE,MIGRATION_DIRTY_FLAG);

cpu_physical_memory_reset_dirty(addr, addr+TARGET_PAGE_SIZE,MASTER_DIRTY_FLAG);

}

Result2.

Stage2’s transfer data is more bigger.

Q3.

I create my own bitmap(Using hyper call and guest’s daemon) and sent it to QEMU. I am trying to reset bitmaps using this bitmap.(Ignore some Guest page’s copying)

I wrote next code, but it doesn’t work. I want to know why.

for (j=0; j<ACTIVE_NSLOTS; j++)// ACTIVE_NSLOTS means my KVM slot number.(0 to 2)

{

const target_phys_addr_t end_addr=(base_gfn[j]+npages[j])<<12;

start_addr=base_gfn[j]<<12;//base_gfn/npages of KVM slot j

while(start_addr < end_addr)

{

const target_phys_addr_t current = get_start_addr(start_addr, end_addr);

if(current == NULL)

{

break;

}