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

From: Leon Romanovsky
Date: Sun Jun 16 2024 - 11:44:39 EST


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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxx>