Re: [Qemu-devel] [PATCH 3/3] memory-device: break the loop if tmp exceed the hinted range

[Wei Yang <richardw.yang@linux.intel.com>]

On Mon, Jul 29, 2019 at 09:49:37AM +0200, David Hildenbrand wrote:
>On 28.07.19 15:13, Wei Yang wrote:
>> The memory-device list built by memory_device_build_list is ordered by
>> its address, this means if the tmp range exceed the hinted range, all
>> the following range will not overlap with it.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> ---
>>  hw/mem/memory-device.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
>> index 413b514586..aea47ab3e8 100644
>> --- a/hw/mem/memory-device.c
>> +++ b/hw/mem/memory-device.c
>> @@ -180,7 +180,7 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
>>                  range_make_empty(&new);
>>                  break;
>>              }
>> -        } else if (!hint) {
>> +        } else if (!hint || range_lob(&tmp) > range_upb(&new)) {
>>              break;
>>          }
>>      }
>> 
>
>Lower bound is inclusive, upper bound is exclusive. Shouldn't this be
>
>range_lob(&tmp) >= range_upb(&new)
>

Per my understanding, a range with start = 0, size = 0x10000, is represented

    [0, 0xffff]

So if I have another range [0xffff, 0x1ffff], they seems to overlap. The range
[0x10000, 0x1ffff] doesn't overlap with [0, 0xffff].

My original comparison looks right. Do I miss some point?

>Also, I wonder if patch #2 is now really needed?
>

Hmm... I think you are right.

I am afraid without Patch #2, the condition check is not that intuitive. Would
this bring some confusion for audience and maintenance?

I am not sure the percentage of occurrence when hint is provided, while the
generated code for check NULL is less than compare two values.

>-- 
>
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
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