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Subject[net-next PATCH 26/27] igb: Update code to better handle incrementing page count
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This patch updates the driver code so that we do bulk updates of the page
reference count instead of just incrementing it by one reference at a time.
The advantage to doing this is that we cut down on atomic operations and
this in turn should give us a slight improvement in cycles per packet. In
addition if we eventually move this over to using build_skb the gains will
be more noticeable.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---
drivers/net/ethernet/intel/igb/igb.h | 7 ++++++-
drivers/net/ethernet/intel/igb/igb_main.c | 24 +++++++++++++++++-------
2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb.h b/drivers/net/ethernet/intel/igb/igb.h
index d11093d..acbc3ab 100644
--- a/drivers/net/ethernet/intel/igb/igb.h
+++ b/drivers/net/ethernet/intel/igb/igb.h
@@ -210,7 +210,12 @@ struct igb_tx_buffer {
struct igb_rx_buffer {
dma_addr_t dma;
struct page *page;
- unsigned int page_offset;
+#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
+ __u32 page_offset;
+#else
+ __u16 page_offset;
+#endif
+ __u16 pagecnt_bias;
};

struct igb_tx_queue_stats {
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index c8c458c..5e66cde 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -3962,7 +3962,8 @@ static void igb_clean_rx_ring(struct igb_ring *rx_ring)
PAGE_SIZE,
DMA_FROM_DEVICE,
DMA_ATTR_SKIP_CPU_SYNC);
- __free_page(buffer_info->page);
+ __page_frag_drain(buffer_info->page, 0,
+ buffer_info->pagecnt_bias);

buffer_info->page = NULL;
}
@@ -6830,13 +6831,15 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
struct page *page,
unsigned int truesize)
{
+ unsigned int pagecnt_bias = rx_buffer->pagecnt_bias--;
+
/* avoid re-using remote pages */
if (unlikely(igb_page_is_reserved(page)))
return false;

#if (PAGE_SIZE < 8192)
/* if we are only owner of page we can reuse it */
- if (unlikely(page_count(page) != 1))
+ if (unlikely(page_ref_count(page) != pagecnt_bias))
return false;

/* flip page offset to other buffer */
@@ -6849,10 +6852,14 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
return false;
#endif

- /* Even if we own the page, we are not allowed to use atomic_set()
- * This would break get_page_unless_zero() users.
+ /* If we have drained the page fragment pool we need to update
+ * the pagecnt_bias and page count so that we fully restock the
+ * number of references the driver holds.
*/
- page_ref_inc(page);
+ if (unlikely(pagecnt_bias == 1)) {
+ page_ref_add(page, USHRT_MAX);
+ rx_buffer->pagecnt_bias = USHRT_MAX;
+ }

return true;
}
@@ -6904,7 +6911,6 @@ static bool igb_add_rx_frag(struct igb_ring *rx_ring,
return true;

/* this page cannot be reused so discard it */
- __free_page(page);
return false;
}

@@ -6975,10 +6981,13 @@ static struct sk_buff *igb_fetch_rx_buffer(struct igb_ring *rx_ring,
/* hand second half of page back to the ring */
igb_reuse_rx_page(rx_ring, rx_buffer);
} else {
- /* we are not reusing the buffer so unmap it */
+ /* We are not reusing the buffer so unmap it and free
+ * any references we are holding to it
+ */
dma_unmap_page_attrs(rx_ring->dev, rx_buffer->dma,
PAGE_SIZE, DMA_FROM_DEVICE,
DMA_ATTR_SKIP_CPU_SYNC);
+ __page_frag_drain(page, 0, rx_buffer->pagecnt_bias);
}

/* clear contents of rx_buffer */
@@ -7252,6 +7261,7 @@ static bool igb_alloc_mapped_page(struct igb_ring *rx_ring,
bi->dma = dma;
bi->page = page;
bi->page_offset = 0;
+ bi->pagecnt_bias = 1;

return true;
}
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