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

[Leon Romanovsky <leon@kernel.org>]

On Fri, Jun 28, 2024 at 03:13:45PM +0000, David Laight wrote:
> From: Leon Romanovsky
> > Sent: 24 June 2024 10:58
> > 
> > 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@oracle.com>
> > > Reviewed-by: Leon Romanovsky <leonro@nvidia.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
> 
> It would be traditional to enclose a negative value in ().
> (Although only 30+ year old compilers would generate unexpected code for
> 	foo-MAX_RECLAIM_NPAGES
> and you have to go back into the 1970s for
> 	foo=MAX_RECLAIM_NPAGES
> to be a problem.)
> 
> > >  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);
> 
> That shouldn't need all the (s32) casts.

#define doesn't have a type, so it is better to be explicit here.

> (I don't think it even needed them before I relaxed the type check.)
> 
> 	David
> 
> > 
> > Thanks
> > 
> > >  	INIT_WORK(&req->work, pages_work_handler);
> > >  	queue_work(dev->priv.pg_wq, &req->work);
> > >  	return NOTIFY_OK;
> > > --
> > > 1.8.3.1
> > >
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)