netdev - Re: [PATCH 1/1] RDMA/mlx5: Release CPU for other processes in mlx5_free_cmd

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Date: Sun, 26 May 2024 18:23:44 +0300
From: Shay Drori <shayd@...dia.com>
To: Anand Khoje <anand.a.khoje@...cle.com>, <linux-rdma@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <moshe@...dia.com>
CC: <rama.nichanamatlu@...cle.com>, <manjunath.b.patil@...cle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] RDMA/mlx5: Release CPU for other processes in
 mlx5_free_cmd_msg()

Hi Anand.

First, the correct Mailing list for this patch is
netdev@...r.kernel.org, please send there the next version.

On 22/05/2024 6:32, Anand Khoje wrote:
> In non FLR context, at times CX-5 requests release of ~8 million device pages.
> This needs humongous number of cmd mailboxes, which to be released once
> the pages are reclaimed. Release of humongous number of cmd mailboxes
> consuming cpu time running into many secs, with non preemptable kernels
> is leading to critical process starving on that cpu’s RQ. To alleviate
> this, this patch relinquishes cpu periodically but conditionally.
> 
> Orabug: 36275016

this doesn't seem relevant

> 
> Signed-off-by: Anand Khoje <anand.a.khoje@...cle.com>
> ---
>   drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
> index 9c21bce..9fbf25d 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
> @@ -1336,16 +1336,23 @@ static struct mlx5_cmd_msg *mlx5_alloc_cmd_msg(struct mlx5_core_dev *dev,
>   	return ERR_PTR(err);
>   }
>   
> +#define RESCHED_MSEC 2


What if you add cond_resched() on every iteration of the loop ? Does it
take much more time to finish 8 Million pages or same ?
If it does matter, maybe 2 ms is too high freq ? 20 ms ? 200 ms ?

Thanks

>   static void mlx5_free_cmd_msg(struct mlx5_core_dev *dev,
>   			      struct mlx5_cmd_msg *msg)
>   {
>   	struct mlx5_cmd_mailbox *head = msg->next;
>   	struct mlx5_cmd_mailbox *next;
> +	unsigned long start_time = jiffies;
>   
>   	while (head) {
>   		next = head->next;
>   		free_cmd_box(dev, head);
>   		head = next;
> +		if (time_after(jiffies, start_time + msecs_to_jiffies(RESCHED_MSEC))) {
> +			mlx5_core_warn_rl(dev, "Spent more than %d msecs, yielding CPU\n", RESCHED_MSEC);
> +			cond_resched();
> +			start_time = jiffies;
> +		}
>   	}
>   	kfree(msg);
>   }