sfc: allocate more RX buffers per page

Allocating 2 buffers per page is insanely inefficient when MTU is 1500
and PAGE_SIZE is 64K (as it usually is on POWER).  Allocate as many as
we can fit, and choose the refill batch size at run-time so that we
still always use a whole page at once.

[bwh: Fix loop condition to allow for compound pages; rebase]
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

4 files changed, 56 insertions, 45 deletions

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index a70c458f3cef..f050248e9fba 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -643,10 +643,6 @@ static void efx_start_datapath(struct efx_nic *efx)
         if (rx_buf_len <= PAGE_SIZE) {
                 efx->rx_scatter = false;
                 efx->rx_buffer_order = 0;
-                if (rx_buf_len <= PAGE_SIZE / 2)
-                        efx->rx_buffer_truesize = PAGE_SIZE / 2;
-                else
-                        efx->rx_buffer_truesize = PAGE_SIZE;
         } else if (efx->type->can_rx_scatter) {
                 BUILD_BUG_ON(sizeof(struct efx_rx_page_state) +
                              EFX_PAGE_IP_ALIGN + EFX_RX_USR_BUF_SIZE >
@@ -654,14 +650,22 @@ static void efx_start_datapath(struct efx_nic *efx)
                 efx->rx_scatter = true;
                 efx->rx_dma_len = EFX_RX_USR_BUF_SIZE;
                 efx->rx_buffer_order = 0;
-                efx->rx_buffer_truesize = PAGE_SIZE / 2;
         } else {
                 efx->rx_scatter = false;
                 efx->rx_buffer_order = get_order(rx_buf_len);
-                efx->rx_buffer_truesize = PAGE_SIZE << efx->rx_buffer_order;
         }
 
-        efx->rx_bufs_per_page = (rx_buf_len <= PAGE_SIZE / 2) ? 2 : 1;
+        efx_rx_config_page_split(efx);
+        if (efx->rx_buffer_order)
+                netif_dbg(efx, drv, efx->net_dev,
+                          "RX buf len=%u; page order=%u batch=%u\n",
+                          efx->rx_dma_len, efx->rx_buffer_order,
+                          efx->rx_pages_per_batch);
+        else
+                netif_dbg(efx, drv, efx->net_dev,
+                          "RX buf len=%u step=%u bpp=%u; page batch=%u\n",
+                          efx->rx_dma_len, efx->rx_page_buf_step,
+                          efx->rx_bufs_per_page, efx->rx_pages_per_batch);
 
         /* RX filters also have scatter-enabled flags */
         if (efx->rx_scatter != old_rx_scatter)
diff --git a/drivers/net/ethernet/sfc/efx.h b/drivers/net/ethernet/sfc/efx.h
index 211da79a65e8..8372da239b43 100644
--- a/drivers/net/ethernet/sfc/efx.h
+++ b/drivers/net/ethernet/sfc/efx.h
@@ -33,6 +33,7 @@ extern int efx_setup_tc(struct net_device *net_dev, u8 num_tc);
 extern unsigned int efx_tx_max_skb_descs(struct efx_nic *efx);
 
 /* RX */
+extern void efx_rx_config_page_split(struct efx_nic *efx);
 extern int efx_probe_rx_queue(struct efx_rx_queue *rx_queue);
 extern void efx_remove_rx_queue(struct efx_rx_queue *rx_queue);
 extern void efx_init_rx_queue(struct efx_rx_queue *rx_queue);
diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index e22e75c8f635..9bd433a095c5 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -825,7 +825,9 @@ struct efx_nic {
         unsigned int rx_dma_len;
         unsigned int rx_buffer_order;
         unsigned int rx_buffer_truesize;
+        unsigned int rx_page_buf_step;
         unsigned int rx_bufs_per_page;
+        unsigned int rx_pages_per_batch;
         u8 rx_hash_key[40];
         u32 rx_indir_table[128];
         bool rx_scatter;
diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 4cc2ba48a912..a948b36c1910 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -25,19 +25,15 @@
 #include "selftest.h"
 #include "workarounds.h"
 
-/* Number of RX descriptors pushed at once. */
-#define EFX_RX_BATCH  8
+/* Preferred number of descriptors to fill at once */
+#define EFX_RX_PREFERRED_BATCH 8U
 
 /* Number of RX buffers to recycle pages for.  When creating the RX page recycle
  * ring, this number is divided by the number of buffers per page to calculate
  * the number of pages to store in the RX page recycle ring.
  */
 #define EFX_RECYCLE_RING_SIZE_IOMMU 4096
-#define EFX_RECYCLE_RING_SIZE_NOIOMMU (2 * EFX_RX_BATCH)
-
-/* Maximum length for an RX descriptor sharing a page */
-#define EFX_RX_HALF_PAGE ((PAGE_SIZE >> 1) - sizeof(struct efx_rx_page_state) \
-                          - EFX_PAGE_IP_ALIGN)
+#define EFX_RECYCLE_RING_SIZE_NOIOMMU (2 * EFX_RX_PREFERRED_BATCH)
 
 /* Size of buffer allocated for skb header area. */
 #define EFX_SKB_HEADERS  64u
@@ -95,6 +91,19 @@ static inline void efx_sync_rx_buffer(struct efx_nic *efx,
                                 DMA_FROM_DEVICE);
 }
 
+void efx_rx_config_page_split(struct efx_nic *efx)
+{
+        efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + EFX_PAGE_IP_ALIGN,
+                                      L1_CACHE_BYTES);
+        efx->rx_bufs_per_page = efx->rx_buffer_order ? 1 :
+                ((PAGE_SIZE - sizeof(struct efx_rx_page_state)) /
+                 efx->rx_page_buf_step);
+        efx->rx_buffer_truesize = (PAGE_SIZE << efx->rx_buffer_order) /
+                efx->rx_bufs_per_page;
+        efx->rx_pages_per_batch = DIV_ROUND_UP(EFX_RX_PREFERRED_BATCH,
+                                               efx->rx_bufs_per_page);
+}
+
 /* Check the RX page recycle ring for a page that can be reused. */
 static struct page *efx_reuse_page(struct efx_rx_queue *rx_queue)
 {
@@ -134,10 +143,10 @@ static struct page *efx_reuse_page(struct efx_rx_queue *rx_queue)
  *
  * @rx_queue:           Efx RX queue
  *
- * This allocates memory for EFX_RX_BATCH receive buffers, maps them for DMA,
- * and populates struct efx_rx_buffers for each one. Return a negative error
- * code or 0 on success. If a single page can be split between two buffers,
- * then the page will either be inserted fully, or not at at all.
+ * This allocates a batch of pages, maps them for DMA, and populates
+ * struct efx_rx_buffers for each one. Return a negative error code or
+ * 0 on success. If a single page can be used for multiple buffers,
+ * then the page will either be inserted fully, or not at all.
  */
 static int efx_init_rx_buffers(struct efx_rx_queue *rx_queue)
 {
@@ -149,10 +158,8 @@ static int efx_init_rx_buffers(struct efx_rx_queue *rx_queue)
         dma_addr_t dma_addr;
         unsigned index, count;
 
-        /* We can split a page between two buffers */
-        BUILD_BUG_ON(EFX_RX_BATCH & 1);
-
-        for (count = 0; count < EFX_RX_BATCH; ++count) {
+        count = 0;
+        do {
                 page = efx_reuse_page(rx_queue);
                 if (page == NULL) {
                         page = alloc_pages(__GFP_COLD | __GFP_COMP | GFP_ATOMIC,
@@ -174,32 +181,26 @@ static int efx_init_rx_buffers(struct efx_rx_queue *rx_queue)
                         state = page_address(page);
                         dma_addr = state->dma_addr;
                 }
-                get_page(page);
 
                 dma_addr += sizeof(struct efx_rx_page_state);
                 page_offset = sizeof(struct efx_rx_page_state);
 
-        split:
-                index = rx_queue->added_count & rx_queue->ptr_mask;
-                rx_buf = efx_rx_buffer(rx_queue, index);
-                rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN;
-                rx_buf->page = page;
-                rx_buf->page_offset = page_offset + EFX_PAGE_IP_ALIGN;
-                rx_buf->len = efx->rx_dma_len;
-                ++rx_queue->added_count;
-
-                if ((~count & 1) && (efx->rx_dma_len <= EFX_RX_HALF_PAGE)) {
-                        /* Use the second half of the page */
-                        get_page(page);
+                do {
+                        index = rx_queue->added_count & rx_queue->ptr_mask;
+                        rx_buf = efx_rx_buffer(rx_queue, index);
+                        rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN;
+                        rx_buf->page = page;
+                        rx_buf->page_offset = page_offset + EFX_PAGE_IP_ALIGN;
+                        rx_buf->len = efx->rx_dma_len;
                         rx_buf->flags = 0;
-                        dma_addr += (PAGE_SIZE >> 1);
-                        page_offset += (PAGE_SIZE >> 1);
-                        ++count;
-                        goto split;
-                }
+                        ++rx_queue->added_count;
+                        get_page(page);
+                        dma_addr += efx->rx_page_buf_step;
+                        page_offset += efx->rx_page_buf_step;
+                } while (page_offset + efx->rx_page_buf_step <= PAGE_SIZE);
 
                 rx_buf->flags = EFX_RX_BUF_LAST_IN_PAGE;
-        }
+        } while (++count < efx->rx_pages_per_batch);
 
         return 0;
 }
@@ -307,7 +308,8 @@ static void efx_recycle_rx_buffers(struct efx_channel *channel,
  */
 void efx_fast_push_rx_descriptors(struct efx_rx_queue *rx_queue)
 {
-        unsigned fill_level;
+        struct efx_nic *efx = rx_queue->efx;
+        unsigned int fill_level, batch_size;
         int space, rc = 0;
 
         /* Calculate current fill level, and exit if we don't need to fill */
@@ -322,8 +324,9 @@ void efx_fast_push_rx_descriptors(struct efx_rx_queue *rx_queue)
                         rx_queue->min_fill = fill_level;
         }
 
+        batch_size = efx->rx_pages_per_batch * efx->rx_bufs_per_page;
         space = rx_queue->max_fill - fill_level;
-        EFX_BUG_ON_PARANOID(space < EFX_RX_BATCH);
+        EFX_BUG_ON_PARANOID(space < batch_size);
 
         netif_vdbg(rx_queue->efx, rx_status, rx_queue->efx->net_dev,
                    "RX queue %d fast-filling descriptor ring from"
@@ -340,7 +343,7 @@ void efx_fast_push_rx_descriptors(struct efx_rx_queue *rx_queue)
                                 efx_schedule_slow_fill(rx_queue);
                         goto out;
                 }
-        } while ((space -= EFX_RX_BATCH) >= EFX_RX_BATCH);
+        } while ((space -= batch_size) >= batch_size);
 
         netif_vdbg(rx_queue->efx, rx_status, rx_queue->efx->net_dev,
                    "RX queue %d fast-filled descriptor ring "
@@ -708,7 +711,8 @@ void efx_init_rx_queue(struct efx_rx_queue *rx_queue)
 
         /* Initialise limit fields */
         max_fill = efx->rxq_entries - EFX_RXD_HEAD_ROOM;
-        max_trigger = max_fill - EFX_RX_BATCH;
+        max_trigger =
+                max_fill - efx->rx_pages_per_batch * efx->rx_bufs_per_page;
         if (rx_refill_threshold != 0) {
                 trigger = max_fill * min(rx_refill_threshold, 100U) / 100U;
                 if (trigger > max_trigger)