Re: [Qemu-devel] [PATCH 13/18] arch_init: adjust ram_save_setup() for migrate_is_localhost

[Lei Li <lilei@linux.vnet.ibm.com>]

On 08/21/2013 06:48 PM, Paolo Bonzini wrote:
> Il 21/08/2013 09:18, Lei Li ha scritto:
>> Send all the ram blocks hooked by save_page, which will copy
>> ram page and MADV_DONTNEED the page just copied.
> You should implement this entirely in the hook.
>
> It will be a little less efficient because of the dirty bitmap overhead,
> but you should aim at having *zero* changes in arch_init.c and migration.c.

Yes, the reason I modify the migration_thread() to have new process that send all
the ram pages in adjusted qemu_savevm_state_begin stage and send device states in
qemu_savevm_device_state stage for localhost migration is to avoid the bitmap thing,
which is a little less efficient just like you mentioned above.

The performance assurance is very important to this feature, our goal is 100ms
of downtime for a 1TB guest.

>
> Paolo
>
>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>> ---
>>   arch_init.c |   19 +++++++++++++------
>>   1 files changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch_init.c b/arch_init.c
>> index 434a4ca..cbbb4db 100644
>> --- a/arch_init.c
>> +++ b/arch_init.c
>> @@ -474,7 +474,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
>>               /* In doubt sent page as normal */
>>               bytes_sent = -1;
>>               ret = ram_control_save_page(f, block->offset,
>> -                               offset, TARGET_PAGE_SIZE, &bytes_sent);
>> +                                        offset, TARGET_PAGE_SIZE, &bytes_sent);
>>   
>>               if (ret != RAM_SAVE_CONTROL_NOT_SUPP) {
>>                   if (ret != RAM_SAVE_CONTROL_DELAYED) {
>> @@ -613,11 +613,13 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>>       RAMBlock *block;
>>       int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
>>   
>> -    migration_bitmap = bitmap_new(ram_pages);
>> -    bitmap_set(migration_bitmap, 0, ram_pages);
>> -    migration_dirty_pages = ram_pages;
>> -    mig_throttle_on = false;
>> -    dirty_rate_high_cnt = 0;
>> +    if (!migrate_is_localhost()) {
>> +        migration_bitmap = bitmap_new(ram_pages);
>> +        bitmap_set(migration_bitmap, 0, ram_pages);
>> +        migration_dirty_pages = ram_pages;
>> +        mig_throttle_on = false;
>> +        dirty_rate_high_cnt = 0;
>> +    }
>>   
>>       if (migrate_use_xbzrle()) {
>>           XBZRLE.cache = cache_init(migrate_xbzrle_cache_size() /
>> @@ -641,6 +643,11 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>>       migration_bitmap_sync();
>>       qemu_mutex_unlock_iothread();
>>   
>> +    if (migrate_is_localhost()) {
>> +        ram_save_blocks(f);
>> +        return 0;
>> +    }
>> +
>>       qemu_put_be64(f, ram_bytes_total() | RAM_SAVE_FLAG_MEM_SIZE);
>>   
>>       QTAILQ_FOREACH(block, &ram_list.blocks, next) {
>>
>


-- 
Lei