Re: [RFC PATCH v1 29/57] net: igb: Remove PAGE_SIZE compile-time constant assumption

[Ryan Roberts <ryan.roberts@arm.com>]

+ Alexei Starovoitov, Daniel Borkmann, Jesper Dangaard Brouer, John Fastabend,
Przemek Kitszel, Tony Nguyen

This was a rather tricky series to get the recipients correct for and my script
did not realize that "supporter" was a pseudonym for "maintainer" so you were
missed off the original post. Appologies!

More context in cover letter:
https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/


On 14/10/2024 11:58, Ryan Roberts wrote:
> To prepare for supporting boot-time page size selection, refactor code
> to remove assumptions about PAGE_SIZE being compile-time constant. Code
> intended to be equivalent when compile-time page size is active.
> 
> Convert CPP conditionals to C conditionals. The compiler will dead code
> strip when doing a compile-time page size build, for the same end
> effect. But this will also work with boot-time page size builds.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
> 
> ***NOTE***
> Any confused maintainers may want to read the cover note here for context:
> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
> 
>  drivers/net/ethernet/intel/igb/igb.h      |  25 ++--
>  drivers/net/ethernet/intel/igb/igb_main.c | 149 +++++++++++-----------
>  2 files changed, 82 insertions(+), 92 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb.h b/drivers/net/ethernet/intel/igb/igb.h
> index 3c2dc7bdebb50..04aeebcd363b3 100644
> --- a/drivers/net/ethernet/intel/igb/igb.h
> +++ b/drivers/net/ethernet/intel/igb/igb.h
> @@ -158,7 +158,6 @@ struct vf_mac_filter {
>   *	 up negative.  In these cases we should fall back to the 3K
>   *	 buffers.
>   */
> -#if (PAGE_SIZE < 8192)
>  #define IGB_MAX_FRAME_BUILD_SKB (IGB_RXBUFFER_1536 - NET_IP_ALIGN)
>  #define IGB_2K_TOO_SMALL_WITH_PADDING \
>  ((NET_SKB_PAD + IGB_TS_HDR_LEN + IGB_RXBUFFER_1536) > SKB_WITH_OVERHEAD(IGB_RXBUFFER_2048))
> @@ -177,6 +176,9 @@ static inline int igb_skb_pad(void)
>  {
>  	int rx_buf_len;
>  
> +	if (PAGE_SIZE >= 8192)
> +		return NET_SKB_PAD + NET_IP_ALIGN;
> +
>  	/* If a 2K buffer cannot handle a standard Ethernet frame then
>  	 * optimize padding for a 3K buffer instead of a 1.5K buffer.
>  	 *
> @@ -196,9 +198,6 @@ static inline int igb_skb_pad(void)
>  }
>  
>  #define IGB_SKB_PAD	igb_skb_pad()
> -#else
> -#define IGB_SKB_PAD	(NET_SKB_PAD + NET_IP_ALIGN)
> -#endif
>  
>  /* How many Rx Buffers do we bundle into one write to the hardware ? */
>  #define IGB_RX_BUFFER_WRITE	16 /* Must be power of 2 */
> @@ -280,7 +279,7 @@ struct igb_tx_buffer {
>  struct igb_rx_buffer {
>  	dma_addr_t dma;
>  	struct page *page;
> -#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
> +#if (BITS_PER_LONG > 32) || (PAGE_SIZE_MAX >= 65536)
>  	__u32 page_offset;
>  #else
>  	__u16 page_offset;
> @@ -403,22 +402,20 @@ enum e1000_ring_flags_t {
>  
>  static inline unsigned int igb_rx_bufsz(struct igb_ring *ring)
>  {
> -#if (PAGE_SIZE < 8192)
> -	if (ring_uses_large_buffer(ring))
> -		return IGB_RXBUFFER_3072;
> +	if (PAGE_SIZE < 8192) {
> +		if (ring_uses_large_buffer(ring))
> +			return IGB_RXBUFFER_3072;
>  
> -	if (ring_uses_build_skb(ring))
> -		return IGB_MAX_FRAME_BUILD_SKB;
> -#endif
> +		if (ring_uses_build_skb(ring))
> +			return IGB_MAX_FRAME_BUILD_SKB;
> +	}
>  	return IGB_RXBUFFER_2048;
>  }
>  
>  static inline unsigned int igb_rx_pg_order(struct igb_ring *ring)
>  {
> -#if (PAGE_SIZE < 8192)
> -	if (ring_uses_large_buffer(ring))
> +	if (PAGE_SIZE < 8192 && ring_uses_large_buffer(ring))
>  		return 1;
> -#endif
>  	return 0;
>  }
>  
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index 1ef4cb871452a..4f2c53dece1a2 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -4797,9 +4797,7 @@ void igb_configure_rx_ring(struct igb_adapter *adapter,
>  static void igb_set_rx_buffer_len(struct igb_adapter *adapter,
>  				  struct igb_ring *rx_ring)
>  {
> -#if (PAGE_SIZE < 8192)
>  	struct e1000_hw *hw = &adapter->hw;
> -#endif
>  
>  	/* set build_skb and buffer size flags */
>  	clear_ring_build_skb_enabled(rx_ring);
> @@ -4810,12 +4808,11 @@ static void igb_set_rx_buffer_len(struct igb_adapter *adapter,
>  
>  	set_ring_build_skb_enabled(rx_ring);
>  
> -#if (PAGE_SIZE < 8192)
> -	if (adapter->max_frame_size > IGB_MAX_FRAME_BUILD_SKB ||
> +	if (PAGE_SIZE < 8192 &&
> +	    (adapter->max_frame_size > IGB_MAX_FRAME_BUILD_SKB ||
>  	    IGB_2K_TOO_SMALL_WITH_PADDING ||
> -	    rd32(E1000_RCTL) & E1000_RCTL_SBP)
> +	    rd32(E1000_RCTL) & E1000_RCTL_SBP))
>  		set_ring_uses_large_buffer(rx_ring);
> -#endif
>  }
>  
>  /**
> @@ -5314,12 +5311,10 @@ static void igb_set_rx_mode(struct net_device *netdev)
>  				     E1000_RCTL_VFE);
>  	wr32(E1000_RCTL, rctl);
>  
> -#if (PAGE_SIZE < 8192)
> -	if (!adapter->vfs_allocated_count) {
> +	if (PAGE_SIZE < 8192 && !adapter->vfs_allocated_count) {
>  		if (adapter->max_frame_size <= IGB_MAX_FRAME_BUILD_SKB)
>  			rlpml = IGB_MAX_FRAME_BUILD_SKB;
>  	}
> -#endif
>  	wr32(E1000_RLPML, rlpml);
>  
>  	/* In order to support SR-IOV and eventually VMDq it is necessary to set
> @@ -5338,11 +5333,10 @@ static void igb_set_rx_mode(struct net_device *netdev)
>  
>  	/* enable Rx jumbo frames, restrict as needed to support build_skb */
>  	vmolr &= ~E1000_VMOLR_RLPML_MASK;
> -#if (PAGE_SIZE < 8192)
> -	if (adapter->max_frame_size <= IGB_MAX_FRAME_BUILD_SKB)
> +	if (PAGE_SIZE < 8192 &&
> +	    adapter->max_frame_size <= IGB_MAX_FRAME_BUILD_SKB)
>  		vmolr |= IGB_MAX_FRAME_BUILD_SKB;
>  	else
> -#endif
>  		vmolr |= MAX_JUMBO_FRAME_SIZE;
>  	vmolr |= E1000_VMOLR_LPE;
>  
> @@ -8435,17 +8429,17 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
>  	if (!dev_page_is_reusable(page))
>  		return false;
>  
> -#if (PAGE_SIZE < 8192)
> -	/* if we are only owner of page we can reuse it */
> -	if (unlikely((rx_buf_pgcnt - pagecnt_bias) > 1))
> -		return false;
> -#else
> +	if (PAGE_SIZE < 8192) {
> +		/* if we are only owner of page we can reuse it */
> +		if (unlikely((rx_buf_pgcnt - pagecnt_bias) > 1))
> +			return false;
> +	} else {
>  #define IGB_LAST_OFFSET \
>  	(SKB_WITH_OVERHEAD(PAGE_SIZE) - IGB_RXBUFFER_2048)
>  
> -	if (rx_buffer->page_offset > IGB_LAST_OFFSET)
> -		return false;
> -#endif
> +		if (rx_buffer->page_offset > IGB_LAST_OFFSET)
> +			return false;
> +	}
>  
>  	/* If we have drained the page fragment pool we need to update
>  	 * the pagecnt_bias and page count so that we fully restock the
> @@ -8473,20 +8467,22 @@ static void igb_add_rx_frag(struct igb_ring *rx_ring,
>  			    struct sk_buff *skb,
>  			    unsigned int size)
>  {
> -#if (PAGE_SIZE < 8192)
> -	unsigned int truesize = igb_rx_pg_size(rx_ring) / 2;
> -#else
> -	unsigned int truesize = ring_uses_build_skb(rx_ring) ?
> +	unsigned int truesize;
> +
> +	if (PAGE_SIZE < 8192)
> +		truesize = igb_rx_pg_size(rx_ring) / 2;
> +	else
> +		truesize = ring_uses_build_skb(rx_ring) ?
>  				SKB_DATA_ALIGN(IGB_SKB_PAD + size) :
>  				SKB_DATA_ALIGN(size);
> -#endif
> +
>  	skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, rx_buffer->page,
>  			rx_buffer->page_offset, size, truesize);
> -#if (PAGE_SIZE < 8192)
> -	rx_buffer->page_offset ^= truesize;
> -#else
> -	rx_buffer->page_offset += truesize;
> -#endif
> +
> +	if (PAGE_SIZE < 8192)
> +		rx_buffer->page_offset ^= truesize;
> +	else
> +		rx_buffer->page_offset += truesize;
>  }
>  
>  static struct sk_buff *igb_construct_skb(struct igb_ring *rx_ring,
> @@ -8494,16 +8490,16 @@ static struct sk_buff *igb_construct_skb(struct igb_ring *rx_ring,
>  					 struct xdp_buff *xdp,
>  					 ktime_t timestamp)
>  {
> -#if (PAGE_SIZE < 8192)
> -	unsigned int truesize = igb_rx_pg_size(rx_ring) / 2;
> -#else
> -	unsigned int truesize = SKB_DATA_ALIGN(xdp->data_end -
> -					       xdp->data_hard_start);
> -#endif
>  	unsigned int size = xdp->data_end - xdp->data;
> +	unsigned int truesize;
>  	unsigned int headlen;
>  	struct sk_buff *skb;
>  
> +	if (PAGE_SIZE < 8192)
> +		truesize = igb_rx_pg_size(rx_ring) / 2;
> +	else
> +		truesize = SKB_DATA_ALIGN(xdp->data_end - xdp->data_hard_start);
> +
>  	/* prefetch first cache line of first page */
>  	net_prefetch(xdp->data);
>  
> @@ -8529,11 +8525,10 @@ static struct sk_buff *igb_construct_skb(struct igb_ring *rx_ring,
>  		skb_add_rx_frag(skb, 0, rx_buffer->page,
>  				(xdp->data + headlen) - page_address(rx_buffer->page),
>  				size, truesize);
> -#if (PAGE_SIZE < 8192)
> -		rx_buffer->page_offset ^= truesize;
> -#else
> -		rx_buffer->page_offset += truesize;
> -#endif
> +		if (PAGE_SIZE < 8192)
> +			rx_buffer->page_offset ^= truesize;
> +		else
> +			rx_buffer->page_offset += truesize;
>  	} else {
>  		rx_buffer->pagecnt_bias++;
>  	}
> @@ -8546,16 +8541,17 @@ static struct sk_buff *igb_build_skb(struct igb_ring *rx_ring,
>  				     struct xdp_buff *xdp,
>  				     ktime_t timestamp)
>  {
> -#if (PAGE_SIZE < 8192)
> -	unsigned int truesize = igb_rx_pg_size(rx_ring) / 2;
> -#else
> -	unsigned int truesize = SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) +
> -				SKB_DATA_ALIGN(xdp->data_end -
> -					       xdp->data_hard_start);
> -#endif
>  	unsigned int metasize = xdp->data - xdp->data_meta;
> +	unsigned int truesize;
>  	struct sk_buff *skb;
>  
> +	if (PAGE_SIZE < 8192)
> +		truesize = igb_rx_pg_size(rx_ring) / 2;
> +	else
> +		truesize = SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) +
> +			   SKB_DATA_ALIGN(xdp->data_end -
> +					  xdp->data_hard_start);
> +
>  	/* prefetch first cache line of first page */
>  	net_prefetch(xdp->data_meta);
>  
> @@ -8575,11 +8571,10 @@ static struct sk_buff *igb_build_skb(struct igb_ring *rx_ring,
>  		skb_hwtstamps(skb)->hwtstamp = timestamp;
>  
>  	/* update buffer offset */
> -#if (PAGE_SIZE < 8192)
> -	rx_buffer->page_offset ^= truesize;
> -#else
> -	rx_buffer->page_offset += truesize;
> -#endif
> +	if (PAGE_SIZE < 8192)
> +		rx_buffer->page_offset ^= truesize;
> +	else
> +		rx_buffer->page_offset += truesize;
>  
>  	return skb;
>  }
> @@ -8634,14 +8629,14 @@ static unsigned int igb_rx_frame_truesize(struct igb_ring *rx_ring,
>  {
>  	unsigned int truesize;
>  
> -#if (PAGE_SIZE < 8192)
> -	truesize = igb_rx_pg_size(rx_ring) / 2; /* Must be power-of-2 */
> -#else
> -	truesize = ring_uses_build_skb(rx_ring) ?
> -		SKB_DATA_ALIGN(IGB_SKB_PAD + size) +
> -		SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) :
> -		SKB_DATA_ALIGN(size);
> -#endif
> +	if (PAGE_SIZE < 8192)
> +		truesize = igb_rx_pg_size(rx_ring) / 2; /* Must be power-of-2 */
> +	else
> +		truesize = ring_uses_build_skb(rx_ring) ?
> +			SKB_DATA_ALIGN(IGB_SKB_PAD + size) +
> +			SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) :
> +			SKB_DATA_ALIGN(size);
> +
>  	return truesize;
>  }
>  
> @@ -8650,11 +8645,11 @@ static void igb_rx_buffer_flip(struct igb_ring *rx_ring,
>  			       unsigned int size)
>  {
>  	unsigned int truesize = igb_rx_frame_truesize(rx_ring, size);
> -#if (PAGE_SIZE < 8192)
> -	rx_buffer->page_offset ^= truesize;
> -#else
> -	rx_buffer->page_offset += truesize;
> -#endif
> +
> +	if (PAGE_SIZE < 8192)
> +		rx_buffer->page_offset ^= truesize;
> +	else
> +		rx_buffer->page_offset += truesize;
>  }
>  
>  static inline void igb_rx_checksum(struct igb_ring *ring,
> @@ -8825,12 +8820,12 @@ static struct igb_rx_buffer *igb_get_rx_buffer(struct igb_ring *rx_ring,
>  	struct igb_rx_buffer *rx_buffer;
>  
>  	rx_buffer = &rx_ring->rx_buffer_info[rx_ring->next_to_clean];
> -	*rx_buf_pgcnt =
> -#if (PAGE_SIZE < 8192)
> -		page_count(rx_buffer->page);
> -#else
> -		0;
> -#endif
> +
> +	if (PAGE_SIZE < 8192)
> +		*rx_buf_pgcnt = page_count(rx_buffer->page);
> +	else
> +		*rx_buf_pgcnt = 0;
> +
>  	prefetchw(rx_buffer->page);
>  
>  	/* we are reusing so sync this buffer for CPU use */
> @@ -8881,9 +8876,8 @@ static int igb_clean_rx_irq(struct igb_q_vector *q_vector, const int budget)
>  	int rx_buf_pgcnt;
>  
>  	/* Frame size depend on rx_ring setup when PAGE_SIZE=4K */
> -#if (PAGE_SIZE < 8192)
> -	frame_sz = igb_rx_frame_truesize(rx_ring, 0);
> -#endif
> +	if (PAGE_SIZE < 8192)
> +		frame_sz = igb_rx_frame_truesize(rx_ring, 0);
>  	xdp_init_buff(&xdp, frame_sz, &rx_ring->xdp_rxq);
>  
>  	while (likely(total_packets < budget)) {
> @@ -8932,10 +8926,9 @@ static int igb_clean_rx_irq(struct igb_q_vector *q_vector, const int budget)
>  
>  			xdp_prepare_buff(&xdp, hard_start, offset, size, true);
>  			xdp_buff_clear_frags_flag(&xdp);
> -#if (PAGE_SIZE > 4096)
>  			/* At larger PAGE_SIZE, frame_sz depend on len size */
> -			xdp.frame_sz = igb_rx_frame_truesize(rx_ring, size);
> -#endif
> +			if (PAGE_SIZE > 4096)
> +				xdp.frame_sz = igb_rx_frame_truesize(rx_ring, size);
>  			skb = igb_run_xdp(adapter, rx_ring, &xdp);
>  		}
>