[PATCH] net: hisilicon: Fix ping latency when deal with high throughput

[PATCH] net: hisilicon: Fix ping latency when deal with high throughput

[Jiangfeng Xiao]

This is due to error in over budget processing.
When dealing with high throughput, the used buffers
that exceeds the budget is not cleaned up. In addition,
it takes a lot of cycles to clean up the used buffer,
and then the buffer where the valid data is located can take effect.

Signed-off-by: Jiangfeng Xiao <xiaojiangfeng@huawei.com>
---
 drivers/net/ethernet/hisilicon/hip04_eth.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
index ad6d912..78f338a 100644
--- a/drivers/net/ethernet/hisilicon/hip04_eth.c
+++ b/drivers/net/ethernet/hisilicon/hip04_eth.c
@@ -575,7 +575,7 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
 	struct hip04_priv *priv = container_of(napi, struct hip04_priv, napi);
 	struct net_device *ndev = priv->ndev;
 	struct net_device_stats *stats = &ndev->stats;
-	unsigned int cnt = hip04_recv_cnt(priv);
+	static unsigned int cnt_remaining;
 	struct rx_desc *desc;
 	struct sk_buff *skb;
 	unsigned char *buf;
@@ -588,8 +588,8 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
 
 	/* clean up tx descriptors */
 	tx_remaining = hip04_tx_reclaim(ndev, false);
-
-	while (cnt && !last) {
+	cnt_remaining += hip04_recv_cnt(priv);
+	while (cnt_remaining && !last) {
 		buf = priv->rx_buf[priv->rx_head];
 		skb = build_skb(buf, priv->rx_buf_size);
 		if (unlikely(!skb)) {
@@ -635,11 +635,13 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
 		hip04_set_recv_desc(priv, phys);
 
 		priv->rx_head = RX_NEXT(priv->rx_head);
-		if (rx >= budget)
+		if (rx >= budget) {
+			--cnt_remaining;
 			goto done;
+		}
 
-		if (--cnt == 0)
-			cnt = hip04_recv_cnt(priv);
+		if (--cnt_remaining == 0)
+			cnt_remaining += hip04_recv_cnt(priv);
 	}
 
 	if (!(priv->reg_inten & RCV_INT)) {
-- 
1.8.5.6

Re: [PATCH] net: hisilicon: Fix ping latency when deal with high throughput

[Joe Perches]

On Sat, 2019-10-26 at 16:49 +0800, Jiangfeng Xiao wrote:
> This is due to error in over budget processing.
> When dealing with high throughput, the used buffers
> that exceeds the budget is not cleaned up. In addition,
> it takes a lot of cycles to clean up the used buffer,
> and then the buffer where the valid data is located can take effect.
[]
> diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
[]
> @@ -575,7 +575,7 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
>  	struct hip04_priv *priv = container_of(napi, struct hip04_priv, napi);
>  	struct net_device *ndev = priv->ndev;
>  	struct net_device_stats *stats = &ndev->stats;
> -	unsigned int cnt = hip04_recv_cnt(priv);
> +	static unsigned int cnt_remaining;

static doesn't seem a great idea here as it's for just a single
driver instance.  Maybe make this part of struct hip04_priv?

Re: [PATCH] net: hisilicon: Fix ping latency when deal with high throughput

[David Miller]

From: Jiangfeng Xiao <xiaojiangfeng@huawei.com>
Date: Sat, 26 Oct 2019 16:49:39 +0800

> diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
> index ad6d912..78f338a 100644
> --- a/drivers/net/ethernet/hisilicon/hip04_eth.c
> +++ b/drivers/net/ethernet/hisilicon/hip04_eth.c
> @@ -575,7 +575,7 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
>  	struct hip04_priv *priv = container_of(napi, struct hip04_priv, napi);
>  	struct net_device *ndev = priv->ndev;
>  	struct net_device_stats *stats = &ndev->stats;
> -	unsigned int cnt = hip04_recv_cnt(priv);
> +	static unsigned int cnt_remaining;

There is no way a piece of software state should be system wide, this is
a per device instance value.

Re: [PATCH] net: hisilicon: Fix ping latency when deal with high throughput

[Jiangfeng Xiao]

On 2019/10/26 23:44, Joe Perches wrote:
> On Sat, 2019-10-26 at 16:49 +0800, Jiangfeng Xiao wrote:
>> This is due to error in over budget processing.
>> When dealing with high throughput, the used buffers
>> that exceeds the budget is not cleaned up. In addition,
>> it takes a lot of cycles to clean up the used buffer,
>> and then the buffer where the valid data is located can take effect.
> []
>> diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
> []
>> @@ -575,7 +575,7 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
>>  	struct hip04_priv *priv = container_of(napi, struct hip04_priv, napi);
>>  	struct net_device *ndev = priv->ndev;
>>  	struct net_device_stats *stats = &ndev->stats;
>> -	unsigned int cnt = hip04_recv_cnt(priv);
>> +	static unsigned int cnt_remaining;
> 
> static doesn't seem a great idea here as it's for just a single
> driver instance.  Maybe make this part of struct hip04_priv?
> 
Thank you for your review. Your suggestion is very good.

Re: [PATCH] net: hisilicon: Fix ping latency when deal with high throughput

[Jiangfeng Xiao]

On 2019/10/27 2:22, David Miller wrote:
> From: Jiangfeng Xiao <xiaojiangfeng@huawei.com>
> Date: Sat, 26 Oct 2019 16:49:39 +0800
> 
>> diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
>> index ad6d912..78f338a 100644
>> --- a/drivers/net/ethernet/hisilicon/hip04_eth.c
>> +++ b/drivers/net/ethernet/hisilicon/hip04_eth.c
>> @@ -575,7 +575,7 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
>>  	struct hip04_priv *priv = container_of(napi, struct hip04_priv, napi);
>>  	struct net_device *ndev = priv->ndev;
>>  	struct net_device_stats *stats = &ndev->stats;
>> -	unsigned int cnt = hip04_recv_cnt(priv);
>> +	static unsigned int cnt_remaining;
> 
> There is no way a piece of software state should be system wide, this is
> a per device instance value.
> 
> .
> 
Thank you for your guidance, I will fix it in v2.