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

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Date: Tue, 18 Jun 2024 23:14:33 +0530
From: Anand Khoje <anand.a.khoje@...cle.com>
To: Leon Romanovsky <leon@...nel.org>
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 6/16/24 21:14, Leon Romanovsky wrote:
> 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>

Hi Leon,

Thanks for providing the R-B. Should I send a v4 with the fix for the 
extra space issue?

-Anand