linux-kernel - Re: [PATCH v3] net/mlx5 : Reclaim max 50K pages at once

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Date: Sun, 16 Jun 2024 18:44:15 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Anand Khoje <anand.a.khoje@...cle.com>
Cc: linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, saeedm@...lanox.com, davem@...emloft.net
Subject: Re: [PATCH v3] net/mlx5 : Reclaim max 50K pages at once

On Fri, Jun 14, 2024 at 01:31:35PM +0530, Anand Khoje wrote:
> In non FLR context, at times CX-5 requests release of ~8 million FW pages.
> This needs humongous number of cmd mailboxes, which to be released once
> the pages are reclaimed. Release of humongous number of cmd mailboxes is
> consuming cpu time running into many seconds. Which with non preemptible
> kernels is leading to critical process starving on that cpu’s RQ.
> To alleviate this, this change restricts the total number of pages
> a worker will try to reclaim maximum 50K pages in one go.
> The limit 50K is aligned with the current firmware capacity/limit of
> releasing 50K pages at once per MLX5_CMD_OP_MANAGE_PAGES + MLX5_PAGES_TAKE
> device command.
> 
> Our tests have shown significant benefit of this change in terms of
> time consumed by dma_pool_free().
> During a test where an event was raised by HCA
> to release 1.3 Million pages, following observations were made:
> 
> - Without this change:
> Number of mailbox messages allocated was around 20K, to accommodate
> the DMA addresses of 1.3 million pages.
> The average time spent by dma_pool_free() to free the DMA pool is between
> 16 usec to 32 usec.
>            value  ------------- Distribution ------------- count
>              256 |                                         0
>              512 |@                                        287
>             1024 |@@@                                      1332
>             2048 |@                                        656
>             4096 |@@@@@                                    2599
>             8192 |@@@@@@@@@@                               4755
>            16384 |@@@@@@@@@@@@@@@                          7545
>            32768 |@@@@@                                    2501
>            65536 |                                         0
> 
> - With this change:
> Number of mailbox messages allocated was around 800; this was to
> accommodate DMA addresses of only 50K pages.
> The average time spent by dma_pool_free() to free the DMA pool in this case
> lies between 1 usec to 2 usec.
>            value  ------------- Distribution ------------- count
>              256 |                                         0
>              512 |@@@@@@@@@@@@@@@@@@                       346
>             1024 |@@@@@@@@@@@@@@@@@@@@@@                   435
>             2048 |                                         0
>             4096 |                                         0
>             8192 |                                         1
>            16384 |                                         0
> 
> Signed-off-by: Anand Khoje <anand.a.khoje@...cle.com>
> ---
> Changes in v3:
>    - Shifted the logic to function req_pages_handler() as per
>      Leon's suggestion.
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 

The title has extra space:
"net/mlx5 : Reclaim max 50K pages at once" -> "net/mlx5: Reclaim max 50K pages at once"

But the code looks good to me.

Thanks,
Reviewed-by: Leon Romanovsky <leonro@...dia.com>