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

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Qiu, Michael
> Sent: Wednesday, December 10, 2014 10:59 AM
> To: Richardson, Bruce
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] Avoid possible memory cpoy when sort hugepages
> 
> 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 :)

I wonder why we do need to write our own bubble sort procedure?
Why we can't use standard qsort() here?
Konstantin

> 
> 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
> >>