Re: [PATCH v6 10/12] migration/dirtyrate: Implement calculate_dirtyrate() function

[David Edmondson <dme@dme.org>]

On Monday, 2020-08-31 at 19:24:04 +08, Zheng Chuan wrote:

> On 2020/8/31 17:13, David Edmondson wrote:
>> On Saturday, 2020-08-29 at 10:52:55 +08, Chuan Zheng wrote:
>> 
>>> Implement calculate_dirtyrate() function.
>>>
>>> Signed-off-by: Chuan Zheng <zhengchuan@huawei.com>
>>> Signed-off-by: YanYing Zhuang <ann.zhuangyanying@huawei.com>
>>> ---
>>>  migration/dirtyrate.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>>>  1 file changed, 43 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
>>> index 850126d..95ee23e 100644
>>> --- a/migration/dirtyrate.c
>>> +++ b/migration/dirtyrate.c
>>> @@ -162,6 +162,21 @@ static void get_ramblock_dirty_info(RAMBlock *block,
>>>      strcpy(info->idstr, qemu_ram_get_idstr(block));
>>>  }
>>>  
>>> +static void free_ramblock_dirty_info(struct RamblockDirtyInfo *infos, int count)
>>> +{
>>> +    int i;
>>> +
>>> +    if (!infos) {
>>> +        return;
>>> +    }
>>> +
>>> +    for (i = 0; i < count; i++) {
>>> +        g_free(infos[i].sample_page_vfn);
>>> +        g_free(infos[i].hash_result);
>>> +    }
>>> +    g_free(infos);
>>> +}
>>> +
>>>  static struct RamblockDirtyInfo *
>>>  alloc_ramblock_dirty_info(int *block_index,
>>>                            struct RamblockDirtyInfo *block_dinfo)
>>> @@ -301,8 +316,34 @@ static int compare_page_hash_info(struct RamblockDirtyInfo *info,
>>>  
>>>  static void calculate_dirtyrate(struct DirtyRateConfig config)
>>>  {
>>> -    /* todo */
>>> -    return;
>>> +    struct RamblockDirtyInfo *block_dinfo = NULL;
>>> +    int block_index = 0;
>>> +    int64_t msec = 0;
>>> +    int64_t initial_time;
>>> +
>>> +    rcu_register_thread();
>>> +    reset_dirtyrate_stat();
>>> +    rcu_read_lock();
>>> +    initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
>>> +    if (record_ramblock_hash_info(&block_dinfo, config, &block_index) < 0) {
>>> +        goto out;
>>> +    }
>>> +    rcu_read_unlock();
>>> +
>>> +    msec = config.sample_period_seconds * 1000;
>>> +    msec = set_sample_page_period(msec, initial_time);
>>> +
>>> +    rcu_read_lock();
>>> +    if (compare_page_hash_info(block_dinfo, block_index) < 0) {
>>> +        goto out;
>>> +    }
>>> +
>>> +    update_dirtyrate(msec);
>>> +
>>> +out:
>>> +    rcu_read_unlock();
>> 
>> This still holds the RCU lock across update_dirtyrate(), which I
>> understood to be unnecessary.
>>It does need to update_dirtyrate if we goto out when erro happens.
> In order to remove update_dirtyrate out of RCU, it need to add flag
> like is_need_update, like:
> if (record_ramblock_hash_info(&block_dinfo, config, &block_index) < 0) {
>          is_need_update = false;
>          goto out;
> }
>
> if (is_need_update)
>     update_dirtyrate(msec);
>
> I doubt it is worth doing that or it will does any hurt if i holds
> the RCU lock across update_dirtyrate()?

Honestly I'm not sure if holding the RCU lock a little longer will be
measurable or not, perhaps someone with more experience will have a
better idea.

>
>>> +    free_ramblock_dirty_info(block_dinfo, block_index + 1);
>>> +    rcu_unregister_thread();
>>>  }
>>>  
>>>  void *get_dirtyrate_thread(void *arg)
>>> -- 
>>> 1.8.3.1
>> 
>> dme.
>> 

dme.
-- 
We wanna wait, but here we go again.