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net/mlx5e: Optimize modulo in mlx5e_select_queue 

To improve the performance of the modulo operation (%), it's replaced by
a subtracting the divisor in a loop. The modulo is used to fix up an
out-of-bounds value that might be returned by netdev_pick_tx or to
convert the queue number to the channel number when num_tcs > 1. Both
situations are unlikely, because XPS is configured not to pick higher
queues (qid >= num_channels) by default, so under normal circumstances
the flow won't go inside the loop, and it will be faster than %.

num_tcs == 8 adds at most 7 iterations to the loop. PTP adds at most 1
iteration to the loop. HTB would add at most 256 iterations (when
num_channels == 1), so there is an additional boundary check in the HTB
flow, which falls back to % if more than 7 iterations are expected.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
This commit is contained in:
Maxim Mikityanskiy 2022-01-25 12:52:59 +02:00 committed by Saeed Mahameed
parent 3c87aedd48
commit 3a9e5fff2a
2 changed files with 24 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
drivers/net/ethernet/mellanox/mlx5/core/en/selq.c
View File

@ -178,7 +178,8 @@ u16 mlx5e_select_queue(struct net_device *dev, struct sk_buff *skb,
* So we can return a txq_ix that matches the channel and
* packet UP.
*/
return txq_ix % selq->num_channels + up * selq->num_channels;
return mlx5e_txq_to_ch_ix(txq_ix, selq->num_channels) +
up * selq->num_channels;
}
if (unlikely(selq->is_htb)) {
@ -198,7 +199,7 @@ u16 mlx5e_select_queue(struct net_device *dev, struct sk_buff *skb,
* Driver to select these queues only at mlx5e_select_ptpsq()
* and mlx5e_select_htb_queue().
*/
return txq_ix % selq->num_channels;
return mlx5e_txq_to_ch_ix_htb(txq_ix, selq->num_channels);
}
/* PTP is enabled */
@ -214,7 +215,7 @@ u16 mlx5e_select_queue(struct net_device *dev, struct sk_buff *skb,
* If netdev_pick_tx() picks ptp_channel, switch to a regular queue,
* because driver should select the PTP only at mlx5e_select_ptpsq().
*/
txq_ix %= selq->num_channels;
txq_ix = mlx5e_txq_to_ch_ix(txq_ix, selq->num_channels);
if (selq->num_tcs <= 1)
return txq_ix;

20
drivers/net/ethernet/mellanox/mlx5/core/en/selq.h
View File

@ -25,6 +25,26 @@ void mlx5e_selq_prepare(struct mlx5e_selq *selq, struct mlx5e_params *params, bo
void mlx5e_selq_apply(struct mlx5e_selq *selq);
void mlx5e_selq_cancel(struct mlx5e_selq *selq);
static inline u16 mlx5e_txq_to_ch_ix(u16 txq, u16 num_channels)
{
while (unlikely(txq >= num_channels))
txq -= num_channels;
return txq;
}
static inline u16 mlx5e_txq_to_ch_ix_htb(u16 txq, u16 num_channels)
{
if (unlikely(txq >= num_channels)) {
if (unlikely(txq >= num_channels << 3))
txq %= num_channels;
else
do
txq -= num_channels;
while (txq >= num_channels);
}
return txq;
}
u16 mlx5e_select_queue(struct net_device *dev, struct sk_buff *skb,
struct net_device *sb_dev);