[PATCH 4.11 15/84] net/mlx5e: Added BW check for DIM decision mechanism

Greg Kroah-Hartman
2017-07-03T13:47:23Z

From: Tal Gilboa <talgi@mellanox.com>

[ Upstream commit c3164d2fc48fd4fa0477ab658b644559c3fe9073 ]

DIM (Dynamically-tuned Interrupt Moderation) is a mechanism designed for
changing the channel interrupt moderation values in order to reduce CPU
overhead for all traffic types.
Until now only interrupt and packet rate were sampled.
We found a scenario on which we get a false indication since a change in
DIM caused more aggregation and reduced packet rate while increasing BW.

We now regard a change as succesfull iff:
current_BW > (prev_BW + threshold) or
current_BW ~= prev_BW and current_PR > (prev_PR + threshold) or
current_BW ~= prev_BW and current_PR ~= prev_PR and
current_IR < (prev_IR - threshold)
Where BW = Bandwidth, PR = Packet rate and IR = Interrupt rate

Improvements (ConnectX-4Lx 25GbE, single RX queue, LRO off)
--------------------------------------------------
packet size | before[Mb/s] | after[Mb/s] | gain |
2B | 343.4 | 359.4 | 4.5% |
16B | 2739.7 | 2814.8 | 2.7% |
64B | 9739 | 10185.3 | 4.5% |

Fixes: cb3c7fd4f839 ("net/mlx5e: Support adaptive RX coalescing")
Signed-off-by: Tal Gilboa <talgi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ethernet/mellanox/mlx5/core/en.h | 2 +
drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c | 41 +++++++++++----------
2 files changed, 24 insertions(+), 19 deletions(-)

--- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
@@ -313,12 +313,14 @@ struct mlx5e_dma_info {

struct mlx5e_rx_am_stats {
int ppms; /* packets per msec */
+ int bpms; /* bytes per msec */
int epms; /* events per msec */
};

struct mlx5e_rx_am_sample {
ktime_t time;
unsigned int pkt_ctr;
+ unsigned int byte_ctr;
u16 event_ctr;
};

--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
@@ -183,28 +183,27 @@ static void mlx5e_am_exit_parking(struct
mlx5e_am_step(am);
}

+#define IS_SIGNIFICANT_DIFF(val, ref) \
+ (((100 * abs((val) - (ref))) / (ref)) > 10) /* more than 10% difference */
+
static int mlx5e_am_stats_compare(struct mlx5e_rx_am_stats *curr,
struct mlx5e_rx_am_stats *prev)
{
- int diff;
-
- if (!prev->ppms)
- return curr->ppms ? MLX5E_AM_STATS_BETTER :
- MLX5E_AM_STATS_SAME;
-
- diff = curr->ppms - prev->ppms;
- if (((100 * abs(diff)) / prev->ppms) > 10) /* more than 10% diff */
- return (diff > 0) ? MLX5E_AM_STATS_BETTER :
- MLX5E_AM_STATS_WORSE;
-
- if (!prev->epms)
- return curr->epms ? MLX5E_AM_STATS_WORSE :
+ if (!prev->bpms)
+ return curr->bpms ? MLX5E_AM_STATS_BETTER :
MLX5E_AM_STATS_SAME;

- diff = curr->epms - prev->epms;
- if (((100 * abs(diff)) / prev->epms) > 10) /* more than 10% diff */
- return (diff < 0) ? MLX5E_AM_STATS_BETTER :
- MLX5E_AM_STATS_WORSE;
+ if (IS_SIGNIFICANT_DIFF(curr->bpms, prev->bpms))
+ return (curr->bpms > prev->bpms) ? MLX5E_AM_STATS_BETTER :
+ MLX5E_AM_STATS_WORSE;
+
+ if (IS_SIGNIFICANT_DIFF(curr->ppms, prev->ppms))
+ return (curr->ppms > prev->ppms) ? MLX5E_AM_STATS_BETTER :
+ MLX5E_AM_STATS_WORSE;
+
+ if (IS_SIGNIFICANT_DIFF(curr->epms, prev->epms))
+ return (curr->epms < prev->epms) ? MLX5E_AM_STATS_BETTER :
+ MLX5E_AM_STATS_WORSE;

return MLX5E_AM_STATS_SAME;
}
@@ -266,6 +265,7 @@ static void mlx5e_am_sample(struct mlx5e
{
s->time = ktime_get();
s->pkt_ctr = rq->stats.packets;
+ s->byte_ctr = rq->stats.bytes;
s->event_ctr = rq->cq.event_ctr;
}

@@ -278,12 +278,15 @@ static void mlx5e_am_calc_stats(struct m
/* u32 holds up to 71 minutes, should be enough */
u32 delta_us = ktime_us_delta(end->time, start->time);
unsigned int npkts = end->pkt_ctr - start->pkt_ctr;
+ unsigned int nbytes = end->byte_ctr - start->byte_ctr;

if (!delta_us)
return;

- curr_stats->ppms = (npkts * USEC_PER_MSEC) / delta_us;
- curr_stats->epms = (MLX5E_AM_NEVENTS * USEC_PER_MSEC) / delta_us;
+ curr_stats->ppms = DIV_ROUND_UP(npkts * USEC_PER_MSEC, delta_us);
+ curr_stats->bpms = DIV_ROUND_UP(nbytes * USEC_PER_MSEC, delta_us);
+ curr_stats->epms = DIV_ROUND_UP(MLX5E_AM_NEVENTS * USEC_PER_MSEC,
+ delta_us);
}

void mlx5e_rx_am_work(struct work_struct *work)