Re: [Qemu-devel] [PATCH 2/2] migration/xbzrle: cleanup the handling cache miss condition

[Wei Yang]

On Fri, Jun 07, 2019 at 08:01:14PM +0100, Dr. David Alan Gilbert wrote:
>* Wei Yang (address@hidden) wrote:
>> For cache miss condition not in last_stage, we need to insert data into
>> cache. When this step succeed, current_data should be updated. While no
>> matter these checks pass or not, -1 is returned.
>> 
>> Based on this, the logic in cache miss handling could be simplified a
>> little.
>> 
>> Signed-off-by: Wei Yang <address@hidden>
>> ---
>>  migration/ram.c | 17 ++++++++---------
>>  1 file changed, 8 insertions(+), 9 deletions(-)
>> 
>> diff --git a/migration/ram.c b/migration/ram.c
>> index 878cd8de7a..67ba075cc4 100644
>> --- a/migration/ram.c
>> +++ b/migration/ram.c
>> @@ -1572,15 +1572,14 @@ static int save_xbzrle_page(RAMState *rs, uint8_t 
>> **current_data,
>>      if (!cache_is_cached(XBZRLE.cache, current_addr,
>>                           ram_counters.dirty_sync_count)) {
>>          xbzrle_counters.cache_miss++;
>> -        if (!last_stage) {
>> -            if (cache_insert(XBZRLE.cache, current_addr, *current_data,
>> -                             ram_counters.dirty_sync_count) == -1) {
>> -                return -1;
>> -            } else {
>> -                /* update *current_data when the page has been
>> -                   inserted into cache */
>> -                *current_data = get_cached_data(XBZRLE.cache, current_addr);
>> -            }
>> +        if (!last_stage &&
>> +            !cache_insert(XBZRLE.cache, current_addr, *current_data,
>> +                          ram_counters.dirty_sync_count)) {
>> +            /*
>> +             * update *current_data when the page has been inserted into
>> +             * cache
>> +             */
>> +            *current_data = get_cached_data(XBZRLE.cache, current_addr);
>
>No this change doesn't gain anything and I find the original easier to
>read.
>
>This function is really subtle, every time I do anything with it I have
>to think really hard about it, so ease of reading is more important.
>

Yep, I agree ease of reading is more important.

Since the original version looks better, I will keep current code. :-)

>Dave
>
>>          }
>>          return -1;
>>      }
>> -- 
>> 2.19.1
>> 
>--
>Dr. David Alan Gilbert / address@hidden / Manchester, UK

-- 
Wei Yang
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