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From: Adrien Mazarguil <adrien.mazarguil@6wind.com>
To: Ophir Munk <ophirmu@mellanox.com>
Cc: dev@dpdk.org, Thomas Monjalon <thomas@monjalon.net>,
	Olga Shern <olgas@mellanox.com>, Matan Azrad <matan@mellanox.com>
Subject: Re: [dpdk-dev] [PATCH v2 5/7] net/mlx4: remove unnecessary variables in Tx burst
Date: Wed, 25 Oct 2017 18:49:52 +0200	[thread overview]
Message-ID: <20171025164952.GI26782@6wind.com> (raw)
In-Reply-To: <1508768520-4810-6-git-send-email-ophirmu@mellanox.com>

Hi Ophir/Matan,

On Mon, Oct 23, 2017 at 02:21:58PM +0000, Ophir Munk wrote:
> From: Matan Azrad <matan@mellanox.com>
> 
> Remove usage of variables which doesn't add new information for
> performance improvement.
> 
> Signed-off-by: Matan Azrad <matan@mellanox.com>

I'm almost 100% sure this commit wasn't validated for performance on its
own. Don't mention "performance improvement" in that case.

If you're removing a couple of local variables for readability, just say
so.

More below.

> ---
>  drivers/net/mlx4/mlx4_rxtx.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/mlx4/mlx4_rxtx.c b/drivers/net/mlx4/mlx4_rxtx.c
> index 014a6d3..e8d9a35 100644
> --- a/drivers/net/mlx4/mlx4_rxtx.c
> +++ b/drivers/net/mlx4/mlx4_rxtx.c
> @@ -285,8 +285,6 @@ mlx4_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
>  	struct txq *txq = (struct txq *)dpdk_txq;
>  	unsigned int elts_head = txq->elts_head;
>  	const unsigned int elts_n = txq->elts_n;
> -	unsigned int elts_comp = 0;
> -	unsigned int bytes_sent = 0;
>  	unsigned int i;
>  	unsigned int max;
>  	struct mlx4_sq *sq = &txq->msq;
> @@ -498,8 +496,7 @@ mlx4_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
>  						       MLX4_BIT_WQE_OWN : 0));
>  		sq->head += nr_txbbs;
>  		elt->buf = buf;
> -		bytes_sent += buf->pkt_len;
> -		++elts_comp;
> +		txq->stats.obytes += buf->pkt_len;
>  		elts_head = elts_head_next;
>  	}
>  	/* Take a shortcut if nothing must be sent. */
> @@ -507,13 +504,12 @@ mlx4_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
>  		return 0;
>  	/* Increment send statistics counters. */
>  	txq->stats.opackets += i;
> -	txq->stats.obytes += bytes_sent;
>  	/* Make sure that descriptors are written before doorbell record. */
>  	rte_wmb();
>  	/* Ring QP doorbell. */
>  	rte_write32(txq->msq.doorbell_qpn, txq->msq.db);
>  	txq->elts_head = elts_head;
> -	txq->elts_comp += elts_comp;
> +	txq->elts_comp += i;
>  	return i;
>  }

For bytes_sent, reading these changes and assuming -O0 with the compiler
attempting to convert the code without reordering/improving things, this
replaces register variables used in a loop with memory operations on a large
structure through a pointer (txq->stats update for every iteration instead
of once at the end).

Are you really sure this is more optimized that way? Although the compiler
likely does it already with -O3, helping it avoid unnecessary memory writes
is good in my opinion.

OK for the removal of redundant elts_comp though. Although I'm pretty sure
once again the compiler didn't wait for this patch to optimize it away.

-- 
Adrien Mazarguil
6WIND

  reply	other threads:[~2017-10-25 16:50 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1508752838-30408-1-git-send-email-ophirmu@mellanox.com>
2017-10-23 14:21 ` [dpdk-dev] [PATCH v2 0/7] net/mlx4: follow-up on new TX datapath introduced in RC1 Ophir Munk
2017-10-23 14:21   ` [dpdk-dev] [PATCH v2 1/7] net/mlx4: remove error flows from Tx fast path Ophir Munk
2017-10-25 16:49     ` Adrien Mazarguil
2017-10-23 14:21   ` [dpdk-dev] [PATCH v2 2/7] net/mlx4: inline more Tx functions Ophir Munk
2017-10-25 16:49     ` Adrien Mazarguil
2017-10-25 21:42       ` Ophir Munk
2017-10-26  7:48         ` Adrien Mazarguil
2017-10-26 14:27           ` Ophir Munk
2017-10-29 19:30             ` Ophir Munk
2017-10-23 14:21   ` [dpdk-dev] [PATCH v2 3/7] net/mlx4: save lkey in big-endian format Ophir Munk
2017-10-23 15:24     ` Nélio Laranjeiro
2017-10-23 14:21   ` [dpdk-dev] [PATCH v2 4/7] net/mlx4: merge Tx path functions Ophir Munk
2017-10-24 13:51     ` Nélio Laranjeiro
2017-10-24 20:36       ` Ophir Munk
2017-10-25  7:50         ` Nélio Laranjeiro
2017-10-26 10:31           ` Matan Azrad
2017-10-26 12:12             ` Nélio Laranjeiro
2017-10-26 12:30               ` Matan Azrad
2017-10-26 13:44                 ` Nélio Laranjeiro
2017-10-26 16:21                   ` Matan Azrad
2017-10-23 14:21   ` [dpdk-dev] [PATCH v2 5/7] net/mlx4: remove unnecessary variables in Tx burst Ophir Munk
2017-10-25 16:49     ` Adrien Mazarguil [this message]
2017-10-23 14:21   ` [dpdk-dev] [PATCH v2 6/7] net/mlx4: improve performance of one Tx segment Ophir Munk
2017-10-25 16:50     ` Adrien Mazarguil
2017-10-23 14:22   ` [dpdk-dev] [PATCH v2 7/7] net/mlx4: separate Tx for multi-segments Ophir Munk
2017-10-25 16:50     ` Adrien Mazarguil
2017-10-30  8:15       ` Ophir Munk
2017-10-30 10:07   ` [dpdk-dev] [PATCH v3 0/7] Tx path improvements Matan Azrad
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 1/7] net/mlx4: remove error flows from Tx fast path Matan Azrad
2017-10-30 14:23       ` Adrien Mazarguil
2017-10-30 18:11         ` Matan Azrad
2017-10-31 10:16           ` Adrien Mazarguil
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 2/7] net/mlx4: associate MR to MP in a short function Matan Azrad
2017-10-30 14:23       ` Adrien Mazarguil
2017-10-31 13:25         ` Ophir Munk
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 3/7] net/mlx4: merge Tx path functions Matan Azrad
2017-10-30 14:23       ` Adrien Mazarguil
2017-10-30 18:12         ` Matan Azrad
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 4/7] net/mlx4: remove completion counter in Tx burst Matan Azrad
2017-10-30 14:23       ` Adrien Mazarguil
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 5/7] net/mlx4: separate Tx segment cases Matan Azrad
2017-10-30 14:23       ` Adrien Mazarguil
2017-10-30 18:23         ` Matan Azrad
2017-10-31 10:17           ` Adrien Mazarguil
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 6/7] net/mlx4: mitigate Tx path memory barriers Matan Azrad
2017-10-30 14:23       ` Adrien Mazarguil
2017-10-30 19:47         ` Matan Azrad
2017-10-31 10:17           ` Adrien Mazarguil
2017-10-31 11:35             ` Matan Azrad
2017-10-31 13:21               ` Adrien Mazarguil
2017-10-30 10:07     ` [dpdk-dev] [PATCH v3 7/7] net/mlx4: remove empty Tx segment support Matan Azrad
2017-10-30 14:24       ` Adrien Mazarguil
2017-10-31 18:21     ` [dpdk-dev] [PATCH v4 0/8] net/mlx4: Tx path improvements Matan Azrad
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 1/8] net/mlx4: remove error flows from Tx fast path Matan Azrad
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 2/8] net/mlx4: associate MR to MP in a short function Matan Azrad
2017-11-02 13:42         ` Adrien Mazarguil
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 3/8] net/mlx4: fix ring wraparound compiler hint Matan Azrad
2017-11-02 13:42         ` Adrien Mazarguil
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 4/8] net/mlx4: merge Tx path functions Matan Azrad
2017-11-02 13:42         ` Adrien Mazarguil
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 5/8] net/mlx4: remove duplicate handling in Tx burst Matan Azrad
2017-11-02 13:42         ` Adrien Mazarguil
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 6/8] net/mlx4: separate Tx segment cases Matan Azrad
2017-11-02 13:43         ` Adrien Mazarguil
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 7/8] net/mlx4: fix HW memory optimizations careless Matan Azrad
2017-11-02 13:43         ` Adrien Mazarguil
2017-10-31 18:21       ` [dpdk-dev] [PATCH v4 8/8] net/mlx4: mitigate Tx path memory barriers Matan Azrad
2017-11-02 13:43         ` Adrien Mazarguil
2017-11-02 13:41       ` [dpdk-dev] [PATCH] net/mlx4: fix missing include Adrien Mazarguil
2017-11-02 20:35         ` Ferruh Yigit
2017-11-02 16:42     ` [dpdk-dev] [PATCH v5 0/8] net/mlx4: Tx path improvements Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 1/8] net/mlx4: remove error flows from Tx fast path Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 2/8] net/mlx4: associate MR to MP in a short function Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 3/8] net/mlx4: fix ring wraparound compiler hint Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 4/8] net/mlx4: merge Tx path functions Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 5/8] net/mlx4: remove duplicate handling in Tx burst Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 6/8] net/mlx4: separate Tx segment cases Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 7/8] net/mlx4: fix HW memory optimizations careless Matan Azrad
2017-11-02 16:42       ` [dpdk-dev] [PATCH v5 8/8] net/mlx4: mitigate Tx path memory barriers Matan Azrad
2017-11-02 17:07       ` [dpdk-dev] [PATCH v5 0/8] net/mlx4: Tx path improvements Adrien Mazarguil
2017-11-02 20:35         ` Ferruh Yigit
2017-11-02 20:41       ` Ferruh Yigit
2017-11-03  9:48         ` Adrien Mazarguil
2017-11-03 19:25       ` Ferruh Yigit

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