Re: [PATCH net-next v2 9/9] ibmvnic: Do not replenish RX buffers after every polling loop

[Thomas Falcon <tlfalcon@linux.ibm.com>]

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On 11/19/20 3:43 AM, ljp wrote:
> On 2020-11-18 19:12, Thomas Falcon wrote:
>> From: "Dwip N. Banerjee" <dnbanerg@us.ibm.com>
>>
>> Reduce the amount of time spent replenishing RX buffers by
>> only doing so once available buffers has fallen under a certain
>> threshold, in this case half of the total number of buffers, or
>> if the polling loop exits before the packets processed is less
>> than its budget.
>>
>> Signed-off-by: Dwip N. Banerjee <dnbanerg@us.ibm.com>
>> ---
>>  drivers/net/ethernet/ibm/ibmvnic.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/ibm/ibmvnic.c
>> b/drivers/net/ethernet/ibm/ibmvnic.c
>> index 96df6d8fa277..9fe43ab0496d 100644
>> --- a/drivers/net/ethernet/ibm/ibmvnic.c
>> +++ b/drivers/net/ethernet/ibm/ibmvnic.c
>> @@ -2537,7 +2537,10 @@ static int ibmvnic_poll(struct napi_struct
>> *napi, int budget)
>>          frames_processed++;
>>      }
>>
>> -    if (adapter->state != VNIC_CLOSING)
>> +    if (adapter->state != VNIC_CLOSING &&
>> + ((atomic_read(&adapter->rx_pool[scrq_num].available) <
>> +          adapter->req_rx_add_entries_per_subcrq / 2) ||
>> +          frames_processed < budget))
>
> 1/2 seems a simple and good algorithm.
> Explaining why "frames_process < budget" is necessary in the commit 
> message
> or source code also helps.
>
Hello, Lijun. The patch author, Dwip Banerjee, suggested the modified 
commit message below:

Reduce the amount of time spent replenishing RX buffers by
only doing so once available buffers has fallen under a certain
threshold, in this case half of the total number of buffers, or
if the polling loop exits before the packets processed is less
than its budget. Non-exhaustion of NAPI budget implies lower
incoming packet pressure, allowing the leeway to refill the buffers
in preparation for any impending burst.

Would such an update require a v3?

>
>>          replenish_rx_pool(adapter, &adapter->rx_pool[scrq_num]);
>>      if (frames_processed < budget) {
>>          if (napi_complete_done(napi, frames_processed)) {

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