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

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

[Anand Khoje]

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@oracle.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(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c b/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
index 1b38397..e7c2d36 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c
@@ -508,6 +508,7 @@ 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)
 {
@@ -539,9 +540,13 @@ 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;
+
 	INIT_WORK(&req->work, pages_work_handler);
 	queue_work(dev->priv.pg_wq, &req->work);
 	return NOTIFY_OK;
-- 
1.8.3.1

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

[Leon Romanovsky]

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@oracle.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@nvidia.com>

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

[Anand Khoje]

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@oracle.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@nvidia.com>

Hi Leon,

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

-Anand

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

[Leon Romanovsky]

On Tue, Jun 18, 2024 at 11:14:33PM +0530, Anand Khoje wrote:
> 
> 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@oracle.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@nvidia.com>
> 
> Hi Leon,
> 
> Thanks for providing the R-B. Should I send a v4 with the fix for the extra
> space issue?

Yes, please.
And run get_maintainer.pl to get the correct email address for the maintainers and ML.
This patch will be applied by netdev maintainers.

Thanks

> 
> -Anand
>