[PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN

[PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN

[Ben Hutchings]

The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
(powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no
need for this optimisation any more.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
---
 drivers/net/ethernet/sfc/efx.c        |    4 ++--
 drivers/net/ethernet/sfc/net_driver.h |   15 +--------------
 drivers/net/ethernet/sfc/rx.c         |    6 +++---
 3 files changed, 6 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index 01b9920..999289b 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -638,13 +638,13 @@ static void efx_start_datapath(struct efx_nic *efx)
 			   EFX_MAX_FRAME_LEN(efx->net_dev->mtu) +
 			   efx->type->rx_buffer_padding);
 	rx_buf_len = (sizeof(struct efx_rx_page_state) +
-		      EFX_PAGE_IP_ALIGN + efx->rx_dma_len);
+		      NET_IP_ALIGN + efx->rx_dma_len);
 	if (rx_buf_len <= PAGE_SIZE) {
 		efx->rx_scatter = false;
 		efx->rx_buffer_order = 0;
 	} 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 >
+			     NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE >
 			     PAGE_SIZE / 2);
 		efx->rx_scatter = true;
 		efx->rx_dma_len = EFX_RX_USR_BUF_SIZE;
diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index 9bd433a..5efddf3 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -468,24 +468,11 @@ enum nic_state {
 };
 
 /*
- * Alignment of page-allocated RX buffers
- *
- * Controls the number of bytes inserted at the start of an RX buffer.
- * This is the equivalent of NET_IP_ALIGN [which controls the alignment
- * of the skb->head for hardware DMA].
- */
-#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
-#define EFX_PAGE_IP_ALIGN 0
-#else
-#define EFX_PAGE_IP_ALIGN NET_IP_ALIGN
-#endif
-
-/*
  * Alignment of the skb->head which wraps a page-allocated RX buffer
  *
  * The skb allocated to wrap an rx_buffer can have this alignment. Since
  * the data is memcpy'd from the rx_buf, it does not need to be equal to
- * EFX_PAGE_IP_ALIGN.
+ * NET_IP_ALIGN.
  */
 #define EFX_PAGE_SKB_ALIGN 2
 
diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index e73e30b..99f70dd 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -93,7 +93,7 @@ static inline void efx_sync_rx_buffer(struct efx_nic *efx,
 
 void efx_rx_config_page_split(struct efx_nic *efx)
 {
-	efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + EFX_PAGE_IP_ALIGN,
+	efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + NET_IP_ALIGN,
 				      L1_CACHE_BYTES);
 	efx->rx_bufs_per_page = efx->rx_buffer_order ? 1 :
 		((PAGE_SIZE - sizeof(struct efx_rx_page_state)) /
@@ -188,9 +188,9 @@ static int efx_init_rx_buffers(struct efx_rx_queue *rx_queue)
 		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->dma_addr = dma_addr + NET_IP_ALIGN;
 			rx_buf->page = page;
-			rx_buf->page_offset = page_offset + EFX_PAGE_IP_ALIGN;
+			rx_buf->page_offset = page_offset + NET_IP_ALIGN;
 			rx_buf->len = efx->rx_dma_len;
 			rx_buf->flags = 0;
 			++rx_queue->added_count;

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

[PATCHv2 net 2/2] sfc: Reduce RX scatter buffer size, and reduce alignment if appropriate

[Ben Hutchings]

efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus
a software structure, each appropriately aligned, into a single page.
Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case
on s390, this assertion fails.

The current scatter buffer size is also not a multiple of 64 or 128,
which are more common cache line sizes.  If we can make both the start
and end of a scatter buffer cache-aligned, this will reduce the need
for read-modify-write operations on inter- processor links.

Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 ==
1792.  (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE
also affects user-level networking where a larger amount of
housekeeping data may be needed.  Although this version of the driver
does not support user-level networking, I prefer to keep scattering
behaviour consistent with the out-of-tree version.)

This still doesn't fix the s390 build because like most architectures
it has NET_IP_ALIGN == 2.  When NET_IP_ALIGN != 0 we cannot achieve
cache line alignment at either the start or end of a scatter buffer,
so there is actually no point in padding the buffers to a multiple of
the cache line size.  All we need is 4-byte alignment of the network
header, so do that.

Adjust the assertions accordingly.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
---
 drivers/net/ethernet/sfc/efx.c        |    6 ++++--
 drivers/net/ethernet/sfc/net_driver.h |   16 ++++++++++++++--
 drivers/net/ethernet/sfc/rx.c         |    2 +-
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index 999289b..39e4cb3 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -643,9 +643,11 @@ static void efx_start_datapath(struct efx_nic *efx)
 		efx->rx_scatter = false;
 		efx->rx_buffer_order = 0;
 	} else if (efx->type->can_rx_scatter) {
+		BUILD_BUG_ON(EFX_RX_USR_BUF_SIZE % L1_CACHE_BYTES);
 		BUILD_BUG_ON(sizeof(struct efx_rx_page_state) +
-			     NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE >
-			     PAGE_SIZE / 2);
+			     2 * ALIGN(NET_IP_ALIGN + EFX_RX_USR_BUF_SIZE,
+				       EFX_RX_BUF_ALIGNMENT) >
+			     PAGE_SIZE);
 		efx->rx_scatter = true;
 		efx->rx_dma_len = EFX_RX_USR_BUF_SIZE;
 		efx->rx_buffer_order = 0;
diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index 5efddf3..39d6bd77 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -72,8 +72,20 @@
 /* Maximum possible MTU the driver supports */
 #define EFX_MAX_MTU (9 * 1024)
 
-/* Size of an RX scatter buffer.  Small enough to pack 2 into a 4K page. */
-#define EFX_RX_USR_BUF_SIZE 1824
+/* Size of an RX scatter buffer.  Small enough to pack 2 into a 4K page,
+ * and should be a multiple of the cache line size.
+ */
+#define EFX_RX_USR_BUF_SIZE	(2048 - 256)
+
+/* If possible, we should ensure cache line alignment at start and end
+ * of every buffer.  Otherwise, we just need to ensure 4-byte
+ * alignment of the network header.
+ */
+#if NET_IP_ALIGN == 0
+#define EFX_RX_BUF_ALIGNMENT	L1_CACHE_BYTES
+#else
+#define EFX_RX_BUF_ALIGNMENT	4
+#endif
 
 /* Forward declare Precision Time Protocol (PTP) support structure. */
 struct efx_ptp_data;
diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 99f70dd..a7dfe36 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -94,7 +94,7 @@ static inline void efx_sync_rx_buffer(struct efx_nic *efx,
 void efx_rx_config_page_split(struct efx_nic *efx)
 {
 	efx->rx_page_buf_step = ALIGN(efx->rx_dma_len + NET_IP_ALIGN,
-				      L1_CACHE_BYTES);
+				      EFX_RX_BUF_ALIGNMENT);
 	efx->rx_bufs_per_page = efx->rx_buffer_order ? 1 :
 		((PAGE_SIZE - sizeof(struct efx_rx_page_state)) /
 		 efx->rx_page_buf_step);

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: [PATCHv2 net 2/2] sfc: Reduce RX scatter buffer size, and reduce alignment if appropriate

[Geert Uytterhoeven]

On Tue, May 14, 2013 at 12:01 AM, Ben Hutchings
<bhutchings@solarflare.com> wrote:
> efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus
> a software structure, each appropriately aligned, into a single page.
> Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case
> on s390, this assertion fails.
>
> The current scatter buffer size is also not a multiple of 64 or 128,
> which are more common cache line sizes.  If we can make both the start
> and end of a scatter buffer cache-aligned, this will reduce the need
> for read-modify-write operations on inter- processor links.
>
> Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 ==
> 1792.  (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE
> also affects user-level networking where a larger amount of
> housekeeping data may be needed.  Although this version of the driver
> does not support user-level networking, I prefer to keep scattering
> behaviour consistent with the out-of-tree version.)
>
> This still doesn't fix the s390 build because like most architectures
> it has NET_IP_ALIGN == 2.  When NET_IP_ALIGN != 0 we cannot achieve
> cache line alignment at either the start or end of a scatter buffer,
> so there is actually no point in padding the buffers to a multiple of
> the cache line size.  All we need is 4-byte alignment of the network
> header, so do that.
>
> Adjust the assertions accordingly.
>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

Fixes the s390 build, so
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCHv2 net 2/2] sfc: Reduce RX scatter buffer size, and reduce alignment if appropriate

[David Miller]

From: Ben Hutchings <bhutchings@solarflare.com>
Date: Mon, 13 May 2013 23:01:22 +0100

> efx_start_datapath() asserts that we can fit 2 RX scatter buffers plus
> a software structure, each appropriately aligned, into a single page.
> Where L1_CACHE_BYTES == 256 and PAGE_SIZE == 4096, which is the case
> on s390, this assertion fails.
> 
> The current scatter buffer size is also not a multiple of 64 or 128,
> which are more common cache line sizes.  If we can make both the start
> and end of a scatter buffer cache-aligned, this will reduce the need
> for read-modify-write operations on inter- processor links.
> 
> Fix the alignment by reducing EFX_RX_USR_BUF_SIZE to 2048 - 256 ==
> 1792.  (We could use 2048 - L1_CACHE_BYTES, but EFX_RX_USR_BUF_SIZE
> also affects user-level networking where a larger amount of
> housekeeping data may be needed.  Although this version of the driver
> does not support user-level networking, I prefer to keep scattering
> behaviour consistent with the out-of-tree version.)
> 
> This still doesn't fix the s390 build because like most architectures
> it has NET_IP_ALIGN == 2.  When NET_IP_ALIGN != 0 we cannot achieve
> cache line alignment at either the start or end of a scatter buffer,
> so there is actually no point in padding the buffers to a multiple of
> the cache line size.  All we need is 4-byte alignment of the network
> header, so do that.
> 
> Adjust the assertions accordingly.
> 
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

Applied.

Re: [PATCHv2 net 2/2] sfc: Reduce RX scatter buffer size, and reduce alignment if appropriate

[Ben Hutchings]

On Mon, 2013-05-13 at 23:01 +0100, Ben Hutchings wrote:
[...]
> This still doesn't fix the s390 build because like most architectures
> it has NET_IP_ALIGN == 2.  When NET_IP_ALIGN != 0 we cannot achieve
> cache line alignment at either the start or end of a scatter buffer,
> so there is actually no point in padding the buffers to a multiple of
> the cache line size.  All we need is 4-byte alignment of the network
> header, so do that.
[...]

I was just thinking about this again.  Do we need to care about
alignment in a page fragment at all?  Won't all the headers be pulled
into the header area before being accessed with any instructions that
would require alignment?  (We aren't using build_skb().)

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

RE: [PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN

[David Laight]

> The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no
> need for this optimisation any more.

Hmmm.... even on x86 there will be a measurable cost
in misaligned accesses - at least for some workloads.

If the DMA is able to write to a mis-aligned buffer and
still perform aligned burst transfers mid-frame then
4n+2 aligning the rx buffer should be a win even on x86.

Note to hardware engineers: add an option to write two
bytes of junk before the rx data :-)

	David

Re: [PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN

[Ben Hutchings]

On Tue, 2013-05-14 at 09:32 +0100, David Laight wrote:
> > The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> > (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no
> > need for this optimisation any more.
> 
> Hmmm.... even on x86 there will be a measurable cost
> in misaligned accesses - at least for some workloads.

When they cross cache-line boundaries, yes.

Maybe napi_get_frags() should be adding the 2 byte offset on all
architectures, as the skbs it allocates are never RX DMA buffers.

> If the DMA is able to write to a mis-aligned buffer and
> still perform aligned burst transfers mid-frame then
> 4n+2 aligning the rx buffer should be a win even on x86.

I don't think so.

> Note to hardware engineers: add an option to write two
> bytes of junk before the rx data :-)

There is some hardware with that option.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: [PATCHv2 net 1/2] sfc: Delete EFX_PAGE_IP_ALIGN, equivalent to NET_IP_ALIGN

[David Miller]

From: Ben Hutchings <bhutchings@solarflare.com>
Date: Mon, 13 May 2013 22:58:31 +0100

> The two architectures that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> (powerpc and x86) now both define NET_IP_ALIGN as 0, so there is no
> need for this optimisation any more.
> 
> Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

Applied.