linux-kernel - Re: [PATCH v4] net/mlx5: Reclaim max 50K pages at once

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Date: Mon, 24 Jun 2024 21:18:50 +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, tariqt@...dia.com,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        davem@...emloft.net
Subject: Re: [PATCH v4] net/mlx5: Reclaim max 50K pages at once


On 6/24/24 15:27, Leon Romanovsky wrote:
> On Wed, Jun 19, 2024 at 06:58:27PM +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>
>> Reviewed-by: Leon Romanovsky <leonro@...dia.com>
>> ---
>> Changes in v4:
>>    - Fixed a nit in patch subject.
>> ---
>>   drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c b/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
>> index dcf58ef..06eee3a 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
>> @@ -608,6 +608,7 @@ enum {
>>   	RELEASE_ALL_PAGES_MASK = 0x4000,
>>   };
>>   
>> +#define MAX_RECLAIM_NPAGES -50000
>>   static int req_pages_handler(struct notifier_block *nb,
>>   			     unsigned long type, void *data)
>>   {
>> @@ -639,9 +640,13 @@ static int req_pages_handler(struct notifier_block *nb,
>>   
>>   	req->dev = dev;
>>   	req->func_id = func_id;
>> -	req->npages = npages;
>>   	req->ec_function = ec_function;
>>   	req->release_all = release_all;
>> +	if (npages < MAX_RECLAIM_NPAGES)
>> +		req->npages = MAX_RECLAIM_NPAGES;
>> +	else
>> +		req->npages = npages;
>> +
> BTW, this can be written as:
> 	req->npages = max_t(s32, npages, MAX_RECLAIM_NPAGES);
>
> Thanks
>
Hi Leon,

Thanks for the suggestion. I have sent a v5 with this change.

-Anand

>>   	INIT_WORK(&req->work, pages_work_handler);
>>   	queue_work(dev->priv.pg_wq, &req->work);
>>   	return NOTIFY_OK;
>> -- 
>> 1.8.3.1
>>