Re: [dpdk-dev] [PATCH] Avoid possible memory cpoy when sort hugepages

["Qiu, Michael" <michael.qiu@intel.com>]

On 12/10/2014 6:41 PM, Richardson, Bruce wrote:
> On Wed, Dec 10, 2014 at 10:25:41AM +0800, Michael Qiu wrote:
>> When the first address is the compared address in the loop,
>> it will also do memory copy, which is meaningless,
>> worse more, when hugepg_tbl is mostly in order. This should
>> be a big deal in large hugepage memory systerm(like hunderd
>> or thousand GB).
> I actually doubt the time taken by this sorting is a significant part of the
> initialization time taken, even for hundreds of GBs of memory. Do you have
> any measurements to confirm this?
> [However, that's not to say that we can't merge in this patch]

I've no hardware env of so huge memory, so I haven't do measurements on
this.

This is not a big improvement, but indeed it may do lots of useless
memory copy in initialize stat.

It could, at least could  save time :)

Thanks,
Michael
>
>
>> Meanwhile smallest_idx never be a value of -1,so remove this check.
>>
>> This patch also includes some coding style fix.
>>
>> Signed-off-by: Michael Qiu <michael.qiu@intel.com>
>> ---
>>  lib/librte_eal/linuxapp/eal/eal_memory.c | 13 +++++--------
>>  1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/librte_eal/linuxapp/eal/eal_memory.c b/lib/librte_eal/linuxapp/eal/eal_memory.c
>> index e6cb919..700aba2 100644
>> --- a/lib/librte_eal/linuxapp/eal/eal_memory.c
>> +++ b/lib/librte_eal/linuxapp/eal/eal_memory.c
>> @@ -678,14 +678,13 @@ error:
>>  static int
>>  sort_by_physaddr(struct hugepage_file *hugepg_tbl, struct hugepage_info *hpi)
>>  {
>> -	unsigned i, j;
>> -	int compare_idx;
>> +	unsigned i, j, compare_idx;
>>  	uint64_t compare_addr;
>>  	struct hugepage_file tmp;
>>  
>>  	for (i = 0; i < hpi->num_pages[0]; i++) {
>>  		compare_addr = 0;
>> -		compare_idx = -1;
>> +		compare_idx = i;
>>  
>>  		/*
>>  		 * browse all entries starting at 'i', and find the
>> @@ -704,11 +703,9 @@ sort_by_physaddr(struct hugepage_file *hugepg_tbl, struct hugepage_info *hpi)
>>  			}
>>  		}
>>  
>> -		/* should not happen */
>> -		if (compare_idx == -1) {
>> -			RTE_LOG(ERR, EAL, "%s(): error in physaddr sorting\n", __func__);
>> -			return -1;
>> -		}
>> +		/* avoid memory copy when the first entry is the compared */
>> +		if (compare_idx == i)
>> +			continue;
>>  
>>  		/* swap the 2 entries in the table */
>>  		memcpy(&tmp, &hugepg_tbl[compare_idx],
>> -- 
>> 1.9.3
>>