Re: [dpdk-dev] [PATCH v1] examples/vm_power_manager: fix overflowed return value

["Hunt, David" <david.hunt@intel.com>]

Hi Anatoly,

On 26/4/2019 11:29 AM, Burakov, Anatoly wrote:
> On 26-Apr-19 9:44 AM, David Hunt wrote:
>> Coverity complains about the return of a value that may
>> possibly overflow because of a multiply. Limit the value
>> so it cannot overflow.
>>
>> Coverity issue: 337677
>> Fixes: 4b1a631b8a ("examples/vm_power: add oob monitoring functions")
>> CC: stable@dpdk.org
>> Signed-off-by: David Hunt <david.hunt@intel.com>
>> ---
>>   examples/vm_power_manager/oob_monitor_x86.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/examples/vm_power_manager/oob_monitor_x86.c 
>> b/examples/vm_power_manager/oob_monitor_x86.c
>> index ebd96b205..2074eec1e 100644
>> --- a/examples/vm_power_manager/oob_monitor_x86.c
>> +++ b/examples/vm_power_manager/oob_monitor_x86.c
>> @@ -99,7 +99,10 @@ apply_policy(int core)
>>           return -1.0;
>>       }
>>   -    ratio = (float)miss_diff * (float)100 / (float)hits_diff;
>> +    ratio = (float)miss_diff / (float)hits_diff;
>> +    if (ratio > 1.0)
>> +        ratio = 1.0;
>> +    ratio *= 100.0f;
>
> It should probably be the other way around - multiply first, then 
> clamp. Also, please use RTE_MIN.
>
I tried that, but coverity still sees an overflow condition. I need to 
clamp first, then multiply. Then coverity is happy.

Also, do you really want me to change to use RTE_MIN? I honestly prefer 
the code as it is.



>>         if (ratio < ci->branch_ratio_threshold)
>>           power_manager_scale_core_min(core);
>>
>
>