netdev - Re: [net-next 05/16] ixgbevf: enable multiple queue support

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Date:	Wed, 25 Mar 2015 11:30:52 -0700
From:	Alexander Duyck <alexander.h.duyck@...hat.com>
To:	Vlad Zolotarov <vladz@...udius-systems.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>, davem@...emloft.net
CC:	Emil Tantilov <emil.s.tantilov@...el.com>, netdev@...r.kernel.org,
	nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com
Subject: Re: [net-next 05/16] ixgbevf: enable multiple queue support

On 03/25/2015 01:44 AM, Vlad Zolotarov wrote:
>
>
> On 02/05/15 11:35, Jeff Kirsher wrote:
>> From: Emil Tantilov <emil.s.tantilov@...el.com>
>>
>> This patch enables multiple queues and RSS support for the VF.
>> Maximum of 2 queues are supported due to available vectors.
>>
>> Signed-off-by: Emil Tantilov <emil.s.tantilov@...el.com>
>> Tested-by: Krishneil Singh <Krishneil.k.singh@...el.com>
>> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
>> ---
>>   drivers/net/ethernet/intel/ixgbevf/ixgbevf.h      |  1 +
>>   drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 22 
>> +++++++++++++++++++---
>>   2 files changed, 20 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h 
>> b/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h
>> index 8c44ab2..65cda34 100644
>> --- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h
>> +++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf.h
>> @@ -124,6 +124,7 @@ struct ixgbevf_ring {
>>     #define MAX_RX_QUEUES IXGBE_VF_MAX_RX_QUEUES
>>   #define MAX_TX_QUEUES IXGBE_VF_MAX_TX_QUEUES
>> +#define IXGBEVF_MAX_RSS_QUEUES 2
>
> According to the MRQE register description in 82599 and x540 specs 2 
> (the value of IXGBEVF_MAX_RSS_QUEUES) is the minimal allowed number of 
> queues in a single pool thus it's a minimal number of VF queues - not 
> the maximal (see more comments on this below).

This is the maximum since the VF only supports 3 interrupts, one for 
mailbox and 2 for queues, and RSS requires an interrupt per queue pair.  
The other possibility is that DCB has been enabled in which case there 
RSS is reduced to one queue pair per pool with one RSS pool for each 
traffic class.

>
>>     #define IXGBEVF_DEFAULT_TXD   1024
>>   #define IXGBEVF_DEFAULT_RXD   512
>> diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c 
>> b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
>> index c9b49bf..815808f 100644
>> --- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
>> +++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
>> @@ -1794,7 +1794,8 @@ static int ixgbevf_configure_dcb(struct 
>> ixgbevf_adapter *adapter)
>>       struct ixgbe_hw *hw = &adapter->hw;
>>       unsigned int def_q = 0;
>>       unsigned int num_tcs = 0;
>> -    unsigned int num_rx_queues = 1;
>> +    unsigned int num_rx_queues = adapter->num_rx_queues;
>> +    unsigned int num_tx_queues = adapter->num_tx_queues;
>>       int err;
>>         spin_lock_bh(&adapter->mbx_lock);
>> @@ -1808,6 +1809,9 @@ static int ixgbevf_configure_dcb(struct 
>> ixgbevf_adapter *adapter)
>>           return err;
>>         if (num_tcs > 1) {
>> +        /* we need only one Tx queue */
>> +        num_tx_queues = 1;
>> +
>>           /* update default Tx ring register index */
>>           adapter->tx_ring[0]->reg_idx = def_q;
>>   @@ -1816,7 +1820,8 @@ static int ixgbevf_configure_dcb(struct 
>> ixgbevf_adapter *adapter)
>>       }
>>         /* if we have a bad config abort request queue reset */
>> -    if (adapter->num_rx_queues != num_rx_queues) {
>> +    if ((adapter->num_rx_queues != num_rx_queues) ||
>> +        (adapter->num_tx_queues != num_tx_queues)) {
>>           /* force mailbox timeout to prevent further messages */
>>           hw->mbx.timeout = 0;
>>   @@ -2181,8 +2186,19 @@ static void ixgbevf_set_num_queues(struct 
>> ixgbevf_adapter *adapter)
>>           return;
>>         /* we need as many queues as traffic classes */
>> -    if (num_tcs > 1)
>> +    if (num_tcs > 1) {
>>           adapter->num_rx_queues = num_tcs;
>> +    } else {
>> +        u16 rss = min_t(u16, num_online_cpus(), 
>> IXGBEVF_MAX_RSS_QUEUES);
>
> Emil,
> Here u ignore the IXGBE_VF_RX_QUEUES value returned the PF (stored in 
> the hw->mac.max_rx_queues). This will accidentally work if PF is 
> driven by a current ixgbe Linux driver but what would happen if HV is 
> not a Linux box? What if HV decides to configure the PSRTYPE[x].RQPL 
> to 0 and decide that VF should be configured with a single queue? I 
> maybe miss something here but the above line seems bogus. Please, comment.

It isn't ignored.  The fact that num_tcs is being tested for checks for 
the one case where the number of RSS queues available would be 1, 
otherwise the hardware will provide at least 2 queues.  If the RETA is 
not configured for 2 queues one of them will not be active, but that 
should not be any sort of actual issue and would be more of an 
administrative choice anyway as it would also limit the PF.

- Alex
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