ACK: [PATCH][SRU][Xenial] i40e/i40evf: Limit TSO to 7 descriptors for payload instead of 8 per packet
Stefan Bader
stefan.bader at canonical.com
Mon Jul 3 15:50:49 UTC 2017
On 27.06.2017 22:56, Jay Vosburgh wrote:
> From: Alexander Duyck <aduyck at mirantis.com>
>
> BugLink: https://bugs.launchpad.net/bugs/1700834
>
> This patch addresses a bug introduced based on my interpretation of the
> XL710 datasheet. Specifically section 8.4.1 states that "A single transmit
> packet may span up to 8 buffers (up to 8 data descriptors per packet
> including both the header and payload buffers)." It then later goes on to
> say that each segment for a TSO obeys the previous rule, however it then
> refers to TSO header and the segment payload buffers.
>
> I believe the actual limit for fragments with TSO and a skbuff that has
> payload data in the header portion of the buffer is actually only 7
> fragments as the skb->data portion counts as 2 buffers, one for the TSO
> header, and one for a segment payload buffer.
>
> Fixes: 2d37490b82af ("i40e/i40evf: Rewrite logic for 8 descriptor per packet check")
> Reported-by: Sowmini Varadhan <sowmini.varadhan at oracle.com>
> Signed-off-by: Alexander Duyck <aduyck at mirantis.com>
> Acked-by: Jesse Brandeburg <jesse.brandeburg at intel.com>
> Tested-by: Sowmini Varadhan <sowmini.varadhan at oracle.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher at intel.com>
> (cherry-picked from 3f3f7cb875c0f621485644d4fd7453b0d37f00e4 upstream)
> Signed-off-by: Jay Vosburgh <jay.vosburgh at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
>
> ---
Cherry-pick limited to specific hw, good test result.
> drivers/net/ethernet/intel/i40e/i40e_txrx.c | 49 +++++++++++++--------------
> drivers/net/ethernet/intel/i40e/i40e_txrx.h | 10 ++++--
> drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 49 +++++++++++++--------------
> drivers/net/ethernet/intel/i40evf/i40e_txrx.h | 10 ++++--
> 4 files changed, 62 insertions(+), 56 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index 9a9bda489c7e..c57476633913 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -2594,35 +2594,34 @@ int __i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
> }
>
> /**
> - * __i40e_chk_linearize - Check if there are more than 8 fragments per packet
> + * __i40e_chk_linearize - Check if there are more than 8 buffers per packet
> * @skb: send buffer
> *
> - * Note: Our HW can't scatter-gather more than 8 fragments to build
> - * a packet on the wire and so we need to figure out the cases where we
> - * need to linearize the skb.
> + * Note: Our HW can't DMA more than 8 buffers to build a packet on the wire
> + * and so we need to figure out the cases where we need to linearize the skb.
> + *
> + * For TSO we need to count the TSO header and segment payload separately.
> + * As such we need to check cases where we have 7 fragments or more as we
> + * can potentially require 9 DMA transactions, 1 for the TSO header, 1 for
> + * the segment payload in the first descriptor, and another 7 for the
> + * fragments.
> **/
> bool __i40e_chk_linearize(struct sk_buff *skb)
> {
> const struct skb_frag_struct *frag, *stale;
> - int gso_size, nr_frags, sum;
> -
> - /* check to see if TSO is enabled, if so we may get a repreive */
> - gso_size = skb_shinfo(skb)->gso_size;
> - if (unlikely(!gso_size))
> - return true;
> + int nr_frags, sum;
>
> - /* no need to check if number of frags is less than 8 */
> + /* no need to check if number of frags is less than 7 */
> nr_frags = skb_shinfo(skb)->nr_frags;
> - if (nr_frags < I40E_MAX_BUFFER_TXD)
> + if (nr_frags < (I40E_MAX_BUFFER_TXD - 1))
> return false;
>
> /* We need to walk through the list and validate that each group
> * of 6 fragments totals at least gso_size. However we don't need
> - * to perform such validation on the first or last 6 since the first
> - * 6 cannot inherit any data from a descriptor before them, and the
> - * last 6 cannot inherit any data from a descriptor after them.
> + * to perform such validation on the last 6 since the last 6 cannot
> + * inherit any data from a descriptor after them.
> */
> - nr_frags -= I40E_MAX_BUFFER_TXD - 1;
> + nr_frags -= I40E_MAX_BUFFER_TXD - 2;
> frag = &skb_shinfo(skb)->frags[0];
>
> /* Initialize size to the negative value of gso_size minus 1. We
> @@ -2631,21 +2630,21 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
> * descriptors for a single transmit as the header and previous
> * fragment are already consuming 2 descriptors.
> */
> - sum = 1 - gso_size;
> + sum = 1 - skb_shinfo(skb)->gso_size;
>
> - /* Add size of frags 1 through 5 to create our initial sum */
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> + /* Add size of frags 0 through 4 to create our initial sum */
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
>
> /* Walk through fragments adding latest fragment, testing it, and
> * then removing stale fragments from the sum.
> */
> stale = &skb_shinfo(skb)->frags[0];
> for (;;) {
> - sum += skb_frag_size(++frag);
> + sum += skb_frag_size(frag++);
>
> /* if sum is negative we failed to make sufficient progress */
> if (sum < 0)
> @@ -2655,7 +2654,7 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
> if (!--nr_frags)
> break;
>
> - sum -= skb_frag_size(++stale);
> + sum -= skb_frag_size(stale++);
> }
>
> return false;
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> index 56009709528a..4464ef8659cf 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> @@ -405,10 +405,14 @@ static inline int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
> **/
> static inline bool i40e_chk_linearize(struct sk_buff *skb, int count)
> {
> - /* we can only support up to 8 data buffers for a single send */
> - if (likely(count <= I40E_MAX_BUFFER_TXD))
> + /* Both TSO and single send will work if count is less than 8 */
> + if (likely(count < I40E_MAX_BUFFER_TXD))
> return false;
>
> - return __i40e_chk_linearize(skb);
> + if (skb_is_gso(skb))
> + return __i40e_chk_linearize(skb);
> +
> + /* we can support up to 8 data buffers for a single send */
> + return count != I40E_MAX_BUFFER_TXD;
> }
> #endif /* _I40E_TXRX_H_ */
> diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
> index 75ce1bb42e94..f0646bc26d04 100644
> --- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
> @@ -1797,35 +1797,34 @@ static void i40e_create_tx_ctx(struct i40e_ring *tx_ring,
> }
>
> /**
> - * __i40evf_chk_linearize - Check if there are more than 8 fragments per packet
> + * __i40evf_chk_linearize - Check if there are more than 8 buffers per packet
> * @skb: send buffer
> *
> - * Note: Our HW can't scatter-gather more than 8 fragments to build
> - * a packet on the wire and so we need to figure out the cases where we
> - * need to linearize the skb.
> + * Note: Our HW can't DMA more than 8 buffers to build a packet on the wire
> + * and so we need to figure out the cases where we need to linearize the skb.
> + *
> + * For TSO we need to count the TSO header and segment payload separately.
> + * As such we need to check cases where we have 7 fragments or more as we
> + * can potentially require 9 DMA transactions, 1 for the TSO header, 1 for
> + * the segment payload in the first descriptor, and another 7 for the
> + * fragments.
> **/
> bool __i40evf_chk_linearize(struct sk_buff *skb)
> {
> const struct skb_frag_struct *frag, *stale;
> - int gso_size, nr_frags, sum;
> -
> - /* check to see if TSO is enabled, if so we may get a repreive */
> - gso_size = skb_shinfo(skb)->gso_size;
> - if (unlikely(!gso_size))
> - return true;
> + int nr_frags, sum;
>
> - /* no need to check if number of frags is less than 8 */
> + /* no need to check if number of frags is less than 7 */
> nr_frags = skb_shinfo(skb)->nr_frags;
> - if (nr_frags < I40E_MAX_BUFFER_TXD)
> + if (nr_frags < (I40E_MAX_BUFFER_TXD - 1))
> return false;
>
> /* We need to walk through the list and validate that each group
> * of 6 fragments totals at least gso_size. However we don't need
> - * to perform such validation on the first or last 6 since the first
> - * 6 cannot inherit any data from a descriptor before them, and the
> - * last 6 cannot inherit any data from a descriptor after them.
> + * to perform such validation on the last 6 since the last 6 cannot
> + * inherit any data from a descriptor after them.
> */
> - nr_frags -= I40E_MAX_BUFFER_TXD - 1;
> + nr_frags -= I40E_MAX_BUFFER_TXD - 2;
> frag = &skb_shinfo(skb)->frags[0];
>
> /* Initialize size to the negative value of gso_size minus 1. We
> @@ -1834,21 +1833,21 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
> * descriptors for a single transmit as the header and previous
> * fragment are already consuming 2 descriptors.
> */
> - sum = 1 - gso_size;
> + sum = 1 - skb_shinfo(skb)->gso_size;
>
> - /* Add size of frags 1 through 5 to create our initial sum */
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> - sum += skb_frag_size(++frag);
> + /* Add size of frags 0 through 4 to create our initial sum */
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
> + sum += skb_frag_size(frag++);
>
> /* Walk through fragments adding latest fragment, testing it, and
> * then removing stale fragments from the sum.
> */
> stale = &skb_shinfo(skb)->frags[0];
> for (;;) {
> - sum += skb_frag_size(++frag);
> + sum += skb_frag_size(frag++);
>
> /* if sum is negative we failed to make sufficient progress */
> if (sum < 0)
> @@ -1858,7 +1857,7 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
> if (!--nr_frags)
> break;
>
> - sum -= skb_frag_size(++stale);
> + sum -= skb_frag_size(stale++);
> }
>
> return false;
> diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
> index c1dd8c5c9666..0429553fe887 100644
> --- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
> +++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
> @@ -395,10 +395,14 @@ static inline int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
> **/
> static inline bool i40e_chk_linearize(struct sk_buff *skb, int count)
> {
> - /* we can only support up to 8 data buffers for a single send */
> - if (likely(count <= I40E_MAX_BUFFER_TXD))
> + /* Both TSO and single send will work if count is less than 8 */
> + if (likely(count < I40E_MAX_BUFFER_TXD))
> return false;
>
> - return __i40evf_chk_linearize(skb);
> + if (skb_is_gso(skb))
> + return __i40evf_chk_linearize(skb);
> +
> + /* we can support up to 8 data buffers for a single send */
> + return count != I40E_MAX_BUFFER_TXD;
> }
> #endif /* _I40E_TXRX_H_ */
>
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