Re: [PATCH] net/gve: fix Rx no mbufs stats counter update

[Levend Sayar <levendsayar@gmail.com>]

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> On 19 Feb 2023, at 20:35, Stephen Hemminger <stephen@networkplumber.org> wrote:
> 
> On Sun, 19 Feb 2023 03:30:59 +0300
> Levend Sayar <levendsayar@gmail.com <mailto:levendsayar@gmail.com>> wrote:
> 
>> rx no_mbufs stats counter update is added for another error case.
>> 
>> Fixes: 4f6b1dd8240c ("net/gve: support basic statistics")
>> Cc: junfeng.guo@intel.com
>> 
>> Signed-off-by: Levend Sayar <levendsayar@gmail.com>
>> ---
>> drivers/net/gve/gve_rx.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/gve/gve_rx.c b/drivers/net/gve/gve_rx.c
>> index 66fbcf3930..b0427731f8 100644
>> --- a/drivers/net/gve/gve_rx.c
>> +++ b/drivers/net/gve/gve_rx.c
>> @@ -24,6 +24,7 @@ gve_rx_refill(struct gve_rx_queue *rxq)
>> 				nmb = rte_pktmbuf_alloc(rxq->mpool);
>> 				if (!nmb)
>> 					break;
>> +
>> 				rxq->sw_ring[idx + i] = nmb;
>> 			}
>> 			if (i != nb_alloc) {
> 
> Looks like accidental whitespace change included in this patch.

LS: Right. Let me correct.

>> @@ -59,9 +60,13 @@ gve_rx_refill(struct gve_rx_queue *rxq)
>> 				nmb = rte_pktmbuf_alloc(rxq->mpool);
>> 				if (!nmb)
>> 					break;
>> +
>> 				rxq->sw_ring[idx + i] = nmb;
>> 			}
>> -			nb_alloc = i;
>> +			if (i != nb_alloc) {
>> +				rxq->no_mbufs += nb_alloc - i;
>> +				nb_alloc = i;
>> +			}
> 
> Would be better to add unlikely() here like:
> 			if (unlikely(i < nb_alloc)) {
> 				rxq->no_mbufs += nb_alloc - i;
> 				nb_alloc = i;
> 			}
> 
> Or eliminate conditional branch in hot path completely.
> 			rxq->no_mbufs += nb_alloc - i;
> 			nb_alloc = i;
> 
> Or better yet refactor code here to use rte_pktmbuf_alloc_bulk() which
> does single ring operation.
> 
>> 		}
>> 		rxq->nb_avail -= nb_alloc;
>> 		next_avail += nb_alloc;

LS: “unlikely” can be added. You’re right. Code already tries to make a bulk allocation first.
If that bulk allocation does not work, it tries to allocate one my one. 

I will supersede this one and create v2.
Thanks Stephen.

Best,
Levend

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