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* [PATCH net-next v2 0/2] Some minor optimization for page pool
@ 2021-08-20  6:56 Yunsheng Lin
  2021-08-20  6:56 ` [PATCH net-next v2 1/2] page_pool: use relaxed atomic for release side accounting Yunsheng Lin
  2021-08-20  6:56 ` [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping Yunsheng Lin
  0 siblings, 2 replies; 9+ messages in thread
From: Yunsheng Lin @ 2021-08-20  6:56 UTC (permalink / raw)
  To: davem, kuba; +Cc: hawk, ilias.apalodimas, netdev, linux-kernel, hkallweit1

Patch 1: Use relaxed atomic for release side accounting
Patch 2: Minor optimize for page_pool_dma_map() function

V2: Remove unnecessary unliky() mark as pointed out by
    Heiner.

Yunsheng Lin (2):
  page_pool: use relaxed atomic for release side accounting
  page_pool: optimize the cpu sync operation when DMA mapping

 net/core/page_pool.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

-- 
2.7.4


^ permalink raw reply	[flat|nested] 9+ messages in thread

* [PATCH net-next v2 1/2] page_pool: use relaxed atomic for release side accounting
  2021-08-20  6:56 [PATCH net-next v2 0/2] Some minor optimization for page pool Yunsheng Lin
@ 2021-08-20  6:56 ` Yunsheng Lin
  2021-08-20  7:12   ` Jesper Dangaard Brouer
  2021-08-20  6:56 ` [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping Yunsheng Lin
  1 sibling, 1 reply; 9+ messages in thread
From: Yunsheng Lin @ 2021-08-20  6:56 UTC (permalink / raw)
  To: davem, kuba; +Cc: hawk, ilias.apalodimas, netdev, linux-kernel, hkallweit1

There is no need to synchronize the account updating, so
use the relaxed atomic to avoid some memory barrier in the
data path.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
 net/core/page_pool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index e140905..1a69784 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -370,7 +370,7 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
 	/* This may be the last page returned, releasing the pool, so
 	 * it is not safe to reference pool afterwards.
 	 */
-	count = atomic_inc_return(&pool->pages_state_release_cnt);
+	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
 	trace_page_pool_state_release(pool, page, count);
 }
 EXPORT_SYMBOL(page_pool_release_page);
-- 
2.7.4


^ permalink raw reply	[flat|nested] 9+ messages in thread

* [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping
  2021-08-20  6:56 [PATCH net-next v2 0/2] Some minor optimization for page pool Yunsheng Lin
  2021-08-20  6:56 ` [PATCH net-next v2 1/2] page_pool: use relaxed atomic for release side accounting Yunsheng Lin
@ 2021-08-20  6:56 ` Yunsheng Lin
  2021-08-20  9:39   ` Ilias Apalodimas
  1 sibling, 1 reply; 9+ messages in thread
From: Yunsheng Lin @ 2021-08-20  6:56 UTC (permalink / raw)
  To: davem, kuba; +Cc: hawk, ilias.apalodimas, netdev, linux-kernel, hkallweit1

If the DMA_ATTR_SKIP_CPU_SYNC is not set, cpu syncing is
also done in dma_map_page_attrs(), so set the attrs according
to pool->p.flags to avoid calling cpu sync function again.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
 net/core/page_pool.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 1a69784..3df5554 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -191,8 +191,12 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
 
 static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 {
+	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
 	dma_addr_t dma;
 
+	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
+		attrs = 0;
+
 	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
 	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
 	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
@@ -200,15 +204,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 	 */
 	dma = dma_map_page_attrs(pool->p.dev, page, 0,
 				 (PAGE_SIZE << pool->p.order),
-				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
+				 pool->p.dma_dir, attrs);
 	if (dma_mapping_error(pool->p.dev, dma))
 		return false;
 
 	page_pool_set_dma_addr(page, dma);
 
-	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
-		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
-
 	return true;
 }
 
-- 
2.7.4


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH net-next v2 1/2] page_pool: use relaxed atomic for release side accounting
  2021-08-20  6:56 ` [PATCH net-next v2 1/2] page_pool: use relaxed atomic for release side accounting Yunsheng Lin
@ 2021-08-20  7:12   ` Jesper Dangaard Brouer
  0 siblings, 0 replies; 9+ messages in thread
From: Jesper Dangaard Brouer @ 2021-08-20  7:12 UTC (permalink / raw)
  To: Yunsheng Lin, davem, kuba
  Cc: brouer, hawk, ilias.apalodimas, netdev, linux-kernel, hkallweit1


On 20/08/2021 08.56, Yunsheng Lin wrote:
> There is no need to synchronize the account updating, so
> use the relaxed atomic to avoid some memory barrier in the
> data path.
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>

LGTM

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>

> ---
>   net/core/page_pool.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index e140905..1a69784 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -370,7 +370,7 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
>   	/* This may be the last page returned, releasing the pool, so
>   	 * it is not safe to reference pool afterwards.
>   	 */
> -	count = atomic_inc_return(&pool->pages_state_release_cnt);
> +	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
>   	trace_page_pool_state_release(pool, page, count);
>   }
>   EXPORT_SYMBOL(page_pool_release_page);
> 


^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping
  2021-08-20  6:56 ` [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping Yunsheng Lin
@ 2021-08-20  9:39   ` Ilias Apalodimas
  2021-08-23  3:56     ` Yunsheng Lin
  0 siblings, 1 reply; 9+ messages in thread
From: Ilias Apalodimas @ 2021-08-20  9:39 UTC (permalink / raw)
  To: Yunsheng Lin; +Cc: davem, kuba, hawk, netdev, linux-kernel, hkallweit1

On Fri, Aug 20, 2021 at 02:56:51PM +0800, Yunsheng Lin wrote:
> If the DMA_ATTR_SKIP_CPU_SYNC is not set, cpu syncing is
> also done in dma_map_page_attrs(), so set the attrs according
> to pool->p.flags to avoid calling cpu sync function again.

Isn't DMA_ATTR_SKIP_CPU_SYNC checked within dma_map_page_attrs() anyway?

Regards
/Ilias
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> ---
>  net/core/page_pool.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 1a69784..3df5554 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -191,8 +191,12 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
>  
>  static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>  {
> +	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
>  	dma_addr_t dma;
>  
> +	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> +		attrs = 0;
> +
>  	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
>  	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
>  	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
> @@ -200,15 +204,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>  	 */
>  	dma = dma_map_page_attrs(pool->p.dev, page, 0,
>  				 (PAGE_SIZE << pool->p.order),
> -				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
> +				 pool->p.dma_dir, attrs);
>  	if (dma_mapping_error(pool->p.dev, dma))
>  		return false;
>  
>  	page_pool_set_dma_addr(page, dma);
>  
> -	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> -		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
> -
>  	return true;
>  }
>  
> -- 
> 2.7.4
> 

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping
  2021-08-20  9:39   ` Ilias Apalodimas
@ 2021-08-23  3:56     ` Yunsheng Lin
  2021-08-23 12:42       ` Ilias Apalodimas
  0 siblings, 1 reply; 9+ messages in thread
From: Yunsheng Lin @ 2021-08-23  3:56 UTC (permalink / raw)
  To: Ilias Apalodimas; +Cc: davem, kuba, hawk, netdev, linux-kernel, hkallweit1

On 2021/8/20 17:39, Ilias Apalodimas wrote:
> On Fri, Aug 20, 2021 at 02:56:51PM +0800, Yunsheng Lin wrote:
>> If the DMA_ATTR_SKIP_CPU_SYNC is not set, cpu syncing is
>> also done in dma_map_page_attrs(), so set the attrs according
>> to pool->p.flags to avoid calling cpu sync function again.
> 
> Isn't DMA_ATTR_SKIP_CPU_SYNC checked within dma_map_page_attrs() anyway?

Yes, the checking in dma_map_page_attrs() should save us from
calling dma_sync_single_for_device() again if we set the attrs
according to "pool->p.flags & PP_FLAG_DMA_SYNC_DEV".

As dma_sync_single_for_device() is EXPORT_SYMBOL()'ed, and
should be a no-op for dma coherent device, so there may be a
function calling overhead for dma coherent device, letting
dma_map_page_attrs() handling the sync seems to avoid the stack
pushing/poping overhead:

https://elixir.bootlin.com/linux/latest/source/kernel/dma/direct.h#L104

The one thing I am not sure about is that the pool->p.offset
and pool->p.max_len are used to decide the sync range before this
patch, while the sync range is the same as the map range when doing
the sync in dma_map_page_attrs().

I assumed the above is not a issue? only sync more than we need?
and it won't hurt the performance?

> 
> Regards
> /Ilias
>>
>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>> ---
>>  net/core/page_pool.c | 9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>> index 1a69784..3df5554 100644
>> --- a/net/core/page_pool.c
>> +++ b/net/core/page_pool.c
>> @@ -191,8 +191,12 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
>>  
>>  static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>>  {
>> +	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
>>  	dma_addr_t dma;
>>  
>> +	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
>> +		attrs = 0;
>> +
>>  	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
>>  	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
>>  	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
>> @@ -200,15 +204,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
>>  	 */
>>  	dma = dma_map_page_attrs(pool->p.dev, page, 0,
>>  				 (PAGE_SIZE << pool->p.order),
>> -				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
>> +				 pool->p.dma_dir, attrs);
>>  	if (dma_mapping_error(pool->p.dev, dma))
>>  		return false;
>>  
>>  	page_pool_set_dma_addr(page, dma);
>>  
>> -	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
>> -		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
>> -
>>  	return true;
>>  }
>>  
>> -- 
>> 2.7.4
>>
> .
> 

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping
  2021-08-23  3:56     ` Yunsheng Lin
@ 2021-08-23 12:42       ` Ilias Apalodimas
  2021-08-24  7:00         ` Yunsheng Lin
  0 siblings, 1 reply; 9+ messages in thread
From: Ilias Apalodimas @ 2021-08-23 12:42 UTC (permalink / raw)
  To: Yunsheng Lin; +Cc: davem, kuba, hawk, netdev, linux-kernel, hkallweit1

On Mon, Aug 23, 2021 at 11:56:48AM +0800, Yunsheng Lin wrote:
> On 2021/8/20 17:39, Ilias Apalodimas wrote:
> > On Fri, Aug 20, 2021 at 02:56:51PM +0800, Yunsheng Lin wrote:
> >> If the DMA_ATTR_SKIP_CPU_SYNC is not set, cpu syncing is
> >> also done in dma_map_page_attrs(), so set the attrs according
> >> to pool->p.flags to avoid calling cpu sync function again.
> > 
> > Isn't DMA_ATTR_SKIP_CPU_SYNC checked within dma_map_page_attrs() anyway?
> 
> Yes, the checking in dma_map_page_attrs() should save us from
> calling dma_sync_single_for_device() again if we set the attrs
> according to "pool->p.flags & PP_FLAG_DMA_SYNC_DEV".

But we aren't syncing anything right now when we allocate the pages since
this is called with DMA_ATTR_SKIP_CPU_SYNC. We are syncing the allocated
range on the end of the function, if the pool was created and was requested
to take care of the mappings for us.

> 
> As dma_sync_single_for_device() is EXPORT_SYMBOL()'ed, and
> should be a no-op for dma coherent device, so there may be a
> function calling overhead for dma coherent device, letting
> dma_map_page_attrs() handling the sync seems to avoid the stack
> pushing/poping overhead:
> 
> https://elixir.bootlin.com/linux/latest/source/kernel/dma/direct.h#L104
> 
> The one thing I am not sure about is that the pool->p.offset
> and pool->p.max_len are used to decide the sync range before this
> patch, while the sync range is the same as the map range when doing
> the sync in dma_map_page_attrs().

I am not sure I am following here. We always sync the entire range as well
in the current code as the mapping function is called with max_len.

> 
> I assumed the above is not a issue? only sync more than we need?
> and it won't hurt the performance?

We can sync more than we need, but if it's a non-coherent architecture,
there's a performance penalty. 

Regards
/Ilias
> 
> > 
> > Regards
> > /Ilias
> >>
> >> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> >> ---
> >>  net/core/page_pool.c | 9 +++++----
> >>  1 file changed, 5 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> >> index 1a69784..3df5554 100644
> >> --- a/net/core/page_pool.c
> >> +++ b/net/core/page_pool.c
> >> @@ -191,8 +191,12 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
> >>  
> >>  static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
> >>  {
> >> +	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
> >>  	dma_addr_t dma;
> >>  
> >> +	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> >> +		attrs = 0;
> >> +
> >>  	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
> >>  	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
> >>  	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
> >> @@ -200,15 +204,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
> >>  	 */
> >>  	dma = dma_map_page_attrs(pool->p.dev, page, 0,
> >>  				 (PAGE_SIZE << pool->p.order),
> >> -				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
> >> +				 pool->p.dma_dir, attrs);
> >>  	if (dma_mapping_error(pool->p.dev, dma))
> >>  		return false;
> >>  
> >>  	page_pool_set_dma_addr(page, dma);
> >>  
> >> -	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
> >> -		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
> >> -
> >>  	return true;
> >>  }
> >>  
> >> -- 
> >> 2.7.4
> >>
> > .
> > 

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping
  2021-08-23 12:42       ` Ilias Apalodimas
@ 2021-08-24  7:00         ` Yunsheng Lin
  2021-08-24  9:04           ` Ilias Apalodimas
  0 siblings, 1 reply; 9+ messages in thread
From: Yunsheng Lin @ 2021-08-24  7:00 UTC (permalink / raw)
  To: Ilias Apalodimas; +Cc: davem, kuba, hawk, netdev, linux-kernel, hkallweit1

On 2021/8/23 20:42, Ilias Apalodimas wrote:
> On Mon, Aug 23, 2021 at 11:56:48AM +0800, Yunsheng Lin wrote:
>> On 2021/8/20 17:39, Ilias Apalodimas wrote:
>>> On Fri, Aug 20, 2021 at 02:56:51PM +0800, Yunsheng Lin wrote:

[..]
>>
>> https://elixir.bootlin.com/linux/latest/source/kernel/dma/direct.h#L104
>>
>> The one thing I am not sure about is that the pool->p.offset
>> and pool->p.max_len are used to decide the sync range before this
>> patch, while the sync range is the same as the map range when doing
>> the sync in dma_map_page_attrs().
> 
> I am not sure I am following here. We always sync the entire range as well
> in the current code as the mapping function is called with max_len.
> 
>>
>> I assumed the above is not a issue? only sync more than we need?
>> and it won't hurt the performance?
> 
> We can sync more than we need, but if it's a non-coherent architecture,
> there's a performance penalty. 

Since I do not have any performance data to prove if there is a
performance penalty for non-coherent architecture, I will drop it:)

> 
> Regards
> /Ilias
>>

^ permalink raw reply	[flat|nested] 9+ messages in thread

* Re: [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping
  2021-08-24  7:00         ` Yunsheng Lin
@ 2021-08-24  9:04           ` Ilias Apalodimas
  0 siblings, 0 replies; 9+ messages in thread
From: Ilias Apalodimas @ 2021-08-24  9:04 UTC (permalink / raw)
  To: Yunsheng Lin, Lorenzo Bianconi
  Cc: David S. Miller, Jakub Kicinski, Jesper Dangaard Brouer,
	Networking, open list, Heiner Kallweit

Hi Yunsheng,

+cc Lorenzo, which has done some tests on non-coherent platforms

On Tue, 24 Aug 2021 at 10:00, Yunsheng Lin <linyunsheng@huawei.com> wrote:
>
> On 2021/8/23 20:42, Ilias Apalodimas wrote:
> > On Mon, Aug 23, 2021 at 11:56:48AM +0800, Yunsheng Lin wrote:
> >> On 2021/8/20 17:39, Ilias Apalodimas wrote:
> >>> On Fri, Aug 20, 2021 at 02:56:51PM +0800, Yunsheng Lin wrote:
>
> [..]
> >>
> >> https://elixir.bootlin.com/linux/latest/source/kernel/dma/direct.h#L104
> >>
> >> The one thing I am not sure about is that the pool->p.offset
> >> and pool->p.max_len are used to decide the sync range before this
> >> patch, while the sync range is the same as the map range when doing
> >> the sync in dma_map_page_attrs().
> >
> > I am not sure I am following here. We always sync the entire range as well
> > in the current code as the mapping function is called with max_len.
> >
> >>
> >> I assumed the above is not a issue? only sync more than we need?
> >> and it won't hurt the performance?
> >
> > We can sync more than we need, but if it's a non-coherent architecture,
> > there's a performance penalty.
>
> Since I do not have any performance data to prove if there is a
> performance penalty for non-coherent architecture, I will drop it:)

I am pretty sure it does affect it.  Unless I am missing something the
patch simply re-arranges calls to avoid calling dma_map_page_attrs()
right?
However since dma_map_page_attrs() won't do anything sync-related
since it's called with DMA_ATTR_SKIP_CPU_SYNC, I doubt calling it will
have any measurable difference.  If there is, we should pick it up.


Regards
/Ilias
>
> >
> > Regards
> > /Ilias
> >>

^ permalink raw reply	[flat|nested] 9+ messages in thread

end of thread, other threads:[~2021-08-24  9:05 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-08-20  6:56 [PATCH net-next v2 0/2] Some minor optimization for page pool Yunsheng Lin
2021-08-20  6:56 ` [PATCH net-next v2 1/2] page_pool: use relaxed atomic for release side accounting Yunsheng Lin
2021-08-20  7:12   ` Jesper Dangaard Brouer
2021-08-20  6:56 ` [PATCH net-next v2 2/2] page_pool: optimize the cpu sync operation when DMA mapping Yunsheng Lin
2021-08-20  9:39   ` Ilias Apalodimas
2021-08-23  3:56     ` Yunsheng Lin
2021-08-23 12:42       ` Ilias Apalodimas
2021-08-24  7:00         ` Yunsheng Lin
2021-08-24  9:04           ` Ilias Apalodimas

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