Message-ID: <481f7799-0f1c-efa3-bf2c-e22961e5f376@intel.com>
Date:   Thu, 6 Oct 2022 09:57:19 -0500
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Joe Damato <jdamato@...tly.com>
CC:     <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
        <kuba@...nel.org>, <davem@...emloft.net>,
        <anthony.l.nguyen@...el.com>, <jesse.brandeburg@...el.com>
Subject: Re: [next-queue v2 2/4] i40e: Record number TXes cleaned during NAPI

On 10/6/2022 8:03 AM, Maciej Fijalkowski wrote:
> On Wed, Oct 05, 2022 at 06:00:24PM -0700, Joe Damato wrote:
>> On Wed, Oct 05, 2022 at 05:31:04PM -0700, Joe Damato wrote:
>>> On Wed, Oct 05, 2022 at 07:16:56PM -0500, Samudrala, Sridhar wrote:
>>>> On 10/5/2022 4:21 PM, Joe Damato wrote:
>>>>> Update i40e_clean_tx_irq to take an out parameter (tx_cleaned) which stores
>>>>> the number TXs cleaned.
>>>>>
>>>>> Likewise, update i40e_clean_xdp_tx_irq and i40e_xmit_zc to do the same.
>>>>>
>>>>> Care has been taken to avoid changing the control flow of any functions
>>>>> involved.
>>>>>
>>>>> Signed-off-by: Joe Damato <jdamato@...tly.com>
>>>>> ---
>>>>>   drivers/net/ethernet/intel/i40e/i40e_txrx.c | 16 +++++++++++-----
>>>>>   drivers/net/ethernet/intel/i40e/i40e_xsk.c  | 15 +++++++++++----
>>>>>   drivers/net/ethernet/intel/i40e/i40e_xsk.h  |  3 ++-
>>>>>   3 files changed, 24 insertions(+), 10 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
>>>>> index b97c95f..a2cc98e 100644
>>>>> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
>>>>> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
>>>>> @@ -923,11 +923,13 @@ void i40e_detect_recover_hung(struct i40e_vsi *vsi)
>>>>>    * @vsi: the VSI we care about
>>>>>    * @tx_ring: Tx ring to clean
>>>>>    * @napi_budget: Used to determine if we are in netpoll
>>>>> + * @tx_cleaned: Out parameter set to the number of TXes cleaned
>>>>>    *
>>>>>    * Returns true if there's any budget left (e.g. the clean is finished)
>>>>>    **/
>>>>>   static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
>>>>> -			      struct i40e_ring *tx_ring, int napi_budget)
>>>>> +			      struct i40e_ring *tx_ring, int napi_budget,
>>>>> +			      unsigned int *tx_cleaned)
>>>>>   {
>>>>>   	int i = tx_ring->next_to_clean;
>>>>>   	struct i40e_tx_buffer *tx_buf;
>>>>> @@ -1026,7 +1028,7 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
>>>>>   	i40e_arm_wb(tx_ring, vsi, budget);
>>>>>   	if (ring_is_xdp(tx_ring))
>>>>> -		return !!budget;
>>>>> +		goto out;
>>>>>   	/* notify netdev of completed buffers */
>>>>>   	netdev_tx_completed_queue(txring_txq(tx_ring),
>>>>> @@ -1048,6 +1050,8 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
>>>>>   		}
>>>>>   	}
>>>>> +out:
>>>>> +	*tx_cleaned = total_packets;
>>>>>   	return !!budget;
>>>>>   }
>>>>> @@ -2689,10 +2693,12 @@ int i40e_napi_poll(struct napi_struct *napi, int budget)
>>>>>   			       container_of(napi, struct i40e_q_vector, napi);
>>>>>   	struct i40e_vsi *vsi = q_vector->vsi;
>>>>>   	struct i40e_ring *ring;
>>>>> +	bool tx_clean_complete = true;
>>>>>   	bool clean_complete = true;
>>>>>   	bool arm_wb = false;
>>>>>   	int budget_per_ring;
>>>>>   	int work_done = 0;
>>>>> +	unsigned int tx_cleaned = 0;
>>>>>   	if (test_bit(__I40E_VSI_DOWN, vsi->state)) {
>>>>>   		napi_complete(napi);
>>>>> @@ -2704,11 +2710,11 @@ int i40e_napi_poll(struct napi_struct *napi, int budget)
>>>>>   	 */
>>>>>   	i40e_for_each_ring(ring, q_vector->tx) {
>>>>>   		bool wd = ring->xsk_pool ?
>>>>> -			  i40e_clean_xdp_tx_irq(vsi, ring) :
>>>>> -			  i40e_clean_tx_irq(vsi, ring, budget);
>>>>> +			  i40e_clean_xdp_tx_irq(vsi, ring, &tx_cleaned) :
>>>>> +			  i40e_clean_tx_irq(vsi, ring, budget, &tx_cleaned);
>>>>>   		if (!wd) {
>>>>> -			clean_complete = false;
>>>>> +			clean_complete = tx_clean_complete = false;
>>>>>   			continue;
>>>>>   		}
>>>>>   		arm_wb |= ring->arm_wb;
>>>>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
>>>>> index 790aaeff..f98ce7e4 100644
>>>>> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
>>>>> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
>>>>> @@ -530,18 +530,22 @@ static void i40e_set_rs_bit(struct i40e_ring *xdp_ring)
>>>>>    * i40e_xmit_zc - Performs zero-copy Tx AF_XDP
>>>>>    * @xdp_ring: XDP Tx ring
>>>>>    * @budget: NAPI budget
>>>>> + * @tx_cleaned: Out parameter of the TX packets processed
>>>>>    *
>>>>>    * Returns true if the work is finished.
>>>>>    **/
>>>>> -static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
>>>>> +static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget,
>>>>> +			 unsigned int *tx_cleaned)
>>>>>   {
>>>>>   	struct xdp_desc *descs = xdp_ring->xsk_pool->tx_descs;
>>>>>   	u32 nb_pkts, nb_processed = 0;
>>>>>   	unsigned int total_bytes = 0;
>>>>>   	nb_pkts = xsk_tx_peek_release_desc_batch(xdp_ring->xsk_pool, budget);
>>>>> -	if (!nb_pkts)
>>>>> +	if (!nb_pkts) {
>>>>> +		*tx_cleaned = 0;
>>>>>   		return true;
>>>>> +	}
>>>>>   	if (xdp_ring->next_to_use + nb_pkts >= xdp_ring->count) {
>>>>>   		nb_processed = xdp_ring->count - xdp_ring->next_to_use;
>>>>> @@ -558,6 +562,7 @@ static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
>>>>>   	i40e_update_tx_stats(xdp_ring, nb_pkts, total_bytes);
>>>>> +	*tx_cleaned = nb_pkts;
>>>> With XDP, I don't think we should count these as tx_cleaned packets. These are transmitted
>>>> packets. The tx_cleaned would be the xsk_frames counter in i40e_clean_xdp_tx_irq
>>>> May be we need 2 counters for xdp.
>>> I think there's two issues you are describing, which are separate in my
>>> mind.
>>>
>>>    1.) The name "tx_cleaned", and
>>>    2.) Whether nb_pkts is the right thing to write as the out param.
>>>
>>> For #1: I'm OK to change the name if that's the blocker here; please
>>> suggest a suitable alternative that you'll accept.
>>>
>>> For #2: nb_pkts is, IMO, the right value to bubble up to the tracepoint because
>>> nb_pkts affects clean_complete in i40e_napi_poll which in turn determines
>>> whether or not polling mode is entered.
>>>
>>> The purpose of the tracepoint is to determine when/why/how you are entering
>>> polling mode, so if nb_pkts plays a role in that calculation, it's the
>>> right number to output.
>> I suppose the alternative is to only fire the tracepoint when *not* in XDP.
>> Then the changes to the XDP stuff can be dropped and a separate set of
>> tracepoints for XDP can be created in the future.
> Let's be clear that it's the AF_XDP quirk that we have in here that actual
> xmit happens within NAPI polling routine.
>
> Sridhar is right with having xsk_frames as tx_cleaned but you're also
> right that nb_pkts affects napi polling. But then if you look at Rx side
> there is an analogous case with buffer allocation affecting napi polling.

To be correct,  I would suggest 2 out parameters to i40e_clean_xdp_tx_irq()
tx_cleaned and xdp_transmitted.  tx_cleaned should be filled in
with xsk_frames. Add xdp_transmitted as an out parameter to i40e_xmit_zc()
and fill it with nb_pkts.

I am not completely clear on the reasoning behind setting clean_complete
based on number of packets transmitted in case of XDP.


>
>> That might reduce the complexity a bit, and will probably still be pretty
>> useful for people tuning their non-XDP workloads.

This option is fine too.

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