[net-next,2/6] i40e: prefetch struct page of Rx buffer conditionally

From: Li RongQing <lirongqing@baidu.com>

page_address() accesses struct page only when WANT_PAGE_VIRTUAL
or HASHED_PAGE_VIRTUAL is defined, otherwise it returns address
based on offset, so we prefetch it conditionally

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/i40e/i40e_txrx.c | 2 ++
 1 file changed, 2 insertions(+)

On Tue, 28 Jul 2020 12:08:38 -0700 Tony Nguyen wrote:
> From: Li RongQing <lirongqing@baidu.com>
> 
> page_address() accesses struct page only when WANT_PAGE_VIRTUAL
> or HASHED_PAGE_VIRTUAL is defined, otherwise it returns address
> based on offset, so we prefetch it conditionally
> 
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
> Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index 3e5c566ceb01..5d408fe26063 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -1953,7 +1953,9 @@ static struct i40e_rx_buffer *i40e_get_rx_buffer(struct i40e_ring *rx_ring,
>  	struct i40e_rx_buffer *rx_buffer;
>  
>  	rx_buffer = i40e_rx_bi(rx_ring, rx_ring->next_to_clean);
> +#if defined(WANT_PAGE_VIRTUAL) || defined(HASHED_PAGE_VIRTUAL)
>  	prefetchw(rx_buffer->page);
> +#endif

Looks like something that belongs in a common header not (potentially
multiple) C sources.

> -----邮件原件-----
> 发件人: Jakub Kicinski [mailto:kuba@kernel.org]
> 发送时间: 2020年7月29日 4:14
> 收件人: Tony Nguyen <anthony.l.nguyen@intel.com>
> 抄送: davem@davemloft.net; Li,Rongqing <lirongqing@baidu.com>;
> netdev@vger.kernel.org; nhorman@redhat.com; sassmann@redhat.com;
> jeffrey.t.kirsher@intel.com; Andrew Bowers <andrewx.bowers@intel.com>
> 主题: Re: [net-next 2/6] i40e: prefetch struct page of Rx buffer conditionally
> 
> On Tue, 28 Jul 2020 12:08:38 -0700 Tony Nguyen wrote:
> > From: Li RongQing <lirongqing@baidu.com>
> >
> > page_address() accesses struct page only when WANT_PAGE_VIRTUAL or
> > HASHED_PAGE_VIRTUAL is defined, otherwise it returns address based on
> > offset, so we prefetch it conditionally
> >
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
> > Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
> > ---
> >  drivers/net/ethernet/intel/i40e/i40e_txrx.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > index 3e5c566ceb01..5d408fe26063 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > @@ -1953,7 +1953,9 @@ static struct i40e_rx_buffer
> *i40e_get_rx_buffer(struct i40e_ring *rx_ring,
> >  	struct i40e_rx_buffer *rx_buffer;
> >
> >  	rx_buffer = i40e_rx_bi(rx_ring, rx_ring->next_to_clean);
> > +#if defined(WANT_PAGE_VIRTUAL) || defined(HASHED_PAGE_VIRTUAL)
> >  	prefetchw(rx_buffer->page);

Maybe I change prefetchw to prefetch.

refcount of rx_buffer page will be added here originally,
so prefetchw is needed, but after commit 1793668c3b8c
("i40e/i40evf: Update code to better handle incrementing page count"),
and refcount is not added everytime, so change prefetchw
as prefetch,

> > +#endif
> 
> Looks like something that belongs in a common header not (potentially
> multiple) C sources.

Not clear, how should I change?

-Li

On Wed, 29 Jul 2020 06:20:47 +0000 Li,Rongqing wrote:
> > Looks like something that belongs in a common header not (potentially
> > multiple) C sources.  
> 
> Not clear, how should I change?

Can you add something like:

static inline void prefetch_page_address(struct page *page)
{
#if defined(WANT_PAGE_VIRTUAL) || defined(HASHED_PAGE_VIRTUAL)
	prefetch(page);
#endif
}

to mm.h or prefetch.h or i40e.h or some other header? That's preferred
over adding #ifs directly in the source code.

> -----邮件原件-----
> 发件人: Jakub Kicinski [mailto:kuba@kernel.org]
> 发送时间: 2020年7月30日 5:20
> 收件人: Li,Rongqing <lirongqing@baidu.com>
> 抄送: Tony Nguyen <anthony.l.nguyen@intel.com>; davem@davemloft.net;
> netdev@vger.kernel.org; nhorman@redhat.com; sassmann@redhat.com;
> jeffrey.t.kirsher@intel.com; Andrew Bowers <andrewx.bowers@intel.com>
> 主题: Re: [net-next 2/6] i40e: prefetch struct page of Rx buffer conditionally
> 
> On Wed, 29 Jul 2020 06:20:47 +0000 Li,Rongqing wrote:
> > > Looks like something that belongs in a common header not
> > > (potentially
> > > multiple) C sources.
> >
> > Not clear, how should I change?
> 
> Can you add something like:
> 
> static inline void prefetch_page_address(struct page *page) { #if
> defined(WANT_PAGE_VIRTUAL) || defined(HASHED_PAGE_VIRTUAL)
> 	prefetch(page);
> #endif
> }
> 
> to mm.h or prefetch.h or i40e.h or some other header? That's preferred over
> adding #ifs directly in the source code.


Thanks, I will send a new version

-Li