diff mbox

[next] ixgbe: Limit use of 2K buffers on architectures with 256B or larger cache lines

Message ID 20170203171601.13255.10335.stgit@localhost.localdomain
State Accepted
Delegated to: Jeff Kirsher
Headers show

Commit Message

Alexander H Duyck Feb. 3, 2017, 5:19 p.m. UTC 
From: Alexander Duyck <alexander.h.duyck@intel.com>

On architectures that have a cache line size larger than 64 Bytes we start
running into issues where the amount of headroom for the frame starts
shrinking.

The size of skb_shared_info on a system with a 64B L1 cache line size is
320.  This increases to 384 with a 128B cache line, and 512 with a 256B
cache line.

In addition the NET_SKB_PAD value increases as well consistent with the
cache line size.  As a result when we get to a 256B cache line as seen on
the s390 we end up 768 bytes used by padding and shared info leaving us
with only 1280 bytes to use for data storage.  On architectures such as
this we should default to using 3K Rx buffers out of a 8K page instead of
trying to do 1.5K buffers out of a 4K page.

To take all of this into account I have added one small check so that we
compare the max_frame to the amount of actual data we can store.  This was
already occurring for igb, but I had overlooked it for ixgbe as it doesn't
have strict limits for 82599 once we enable jumbo frames.  By adding this
check we will automatically enable 3K Rx buffers as soon as the maximum
frame size we can handle drops below the standard Ethernet MTU.

I also went through and fixed one small typo that I found where I had left
an IGB in a variable name due to a copy/paste error.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
---

Testing Hints:
	If at all possible it would be best to try testing this patch on
	some other architectures such as PPC64.  In lieu of that just build
	testing via the kernel build robot will probably have to do.  The
	only architecture I can identify that might actually have an issue
	that this fixes is s390 which last I knew there was none of in the
	labs at Intel for testing.

	Basic Rx testing will suffice otherwise.

	Also I am okay with this patch just being merged into the earlier
	patch "ixgbe: Add support for padding packet" if you want to go
	that route.  I just figured it wasn't worth the trouble to resend
	the entire set for a minor issue.

 drivers/net/ethernet/intel/ixgbe/ixgbe.h      |    2 +-
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

Comments

Bowers, AndrewX Feb. 14, 2017, 7:40 p.m. UTC | #1 
> -----Original Message-----
> From: Intel-wired-lan [mailto:intel-wired-lan-bounces@lists.osuosl.org] On
> Behalf Of Alexander Duyck
> Sent: Friday, February 03, 2017 9:20 AM
> To: intel-wired-lan@lists.osuosl.org; Kirsher, Jeffrey T
> <jeffrey.t.kirsher@intel.com>
> Subject: [Intel-wired-lan] [next PATCH] ixgbe: Limit use of 2K buffers on
> architectures with 256B or larger cache lines
> 
> From: Alexander Duyck <alexander.h.duyck@intel.com>
> 
> On architectures that have a cache line size larger than 64 Bytes we start
> running into issues where the amount of headroom for the frame starts
> shrinking.
> 
> The size of skb_shared_info on a system with a 64B L1 cache line size is 320.
> This increases to 384 with a 128B cache line, and 512 with a 256B cache line.
> 
> In addition the NET_SKB_PAD value increases as well consistent with the
> cache line size.  As a result when we get to a 256B cache line as seen on the
> s390 we end up 768 bytes used by padding and shared info leaving us with
> only 1280 bytes to use for data storage.  On architectures such as this we
> should default to using 3K Rx buffers out of a 8K page instead of trying to do
> 1.5K buffers out of a 4K page.
> 
> To take all of this into account I have added one small check so that we
> compare the max_frame to the amount of actual data we can store.  This was
> already occurring for igb, but I had overlooked it for ixgbe as it doesn't have
> strict limits for 82599 once we enable jumbo frames.  By adding this check we
> will automatically enable 3K Rx buffers as soon as the maximum frame size
> we can handle drops below the standard Ethernet MTU.
> 
> I also went through and fixed one small typo that I found where I had left an
> IGB in a variable name due to a copy/paste error.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> ---
> 
> Testing Hints:
> 	If at all possible it would be best to try testing this patch on
> 	some other architectures such as PPC64.  In lieu of that just build
> 	testing via the kernel build robot will probably have to do.  The
> 	only architecture I can identify that might actually have an issue
> 	that this fixes is s390 which last I knew there was none of in the
> 	labs at Intel for testing.
> 
> 	Basic Rx testing will suffice otherwise.
> 
> 	Also I am okay with this patch just being merged into the earlier
> 	patch "ixgbe: Add support for padding packet" if you want to go
> 	that route.  I just figured it wasn't worth the trouble to resend
> 	the entire set for a minor issue.
> 
>  drivers/net/ethernet/intel/ixgbe/ixgbe.h      |    2 +-
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)

Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
diff mbox

Patch

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index 3537d07b4807..77bf71db85af 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -99,7 +99,7 @@ 
 #define IXGBE_MAX_FRAME_BUILD_SKB \
 	(SKB_WITH_OVERHEAD(IXGBE_RXBUFFER_2K) - IXGBE_SKB_PAD)
 #else
-#define IGB_MAX_FRAME_BUILD_SKB IXGBE_RXBUFFER_2K
+#define IXGBE_MAX_FRAME_BUILD_SKB IXGBE_RXBUFFER_2K
 #endif
 
 /*
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 787cee9c59d3..bfcdc2fdeae4 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -4009,7 +4009,8 @@  static void ixgbe_set_rx_buffer_len(struct ixgbe_adapter *adapter)
 		if (adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED)
 			set_bit(__IXGBE_RX_3K_BUFFER, &rx_ring->state);
 
-		if (max_frame > (ETH_FRAME_LEN + ETH_FCS_LEN))
+		if ((max_frame > (ETH_FRAME_LEN + ETH_FCS_LEN)) ||
+		    (max_frame > IXGBE_MAX_FRAME_BUILD_SKB))
 			set_bit(__IXGBE_RX_3K_BUFFER, &rx_ring->state);
 #endif
 	}