Xen devel - Nov 2006 - [PATCH] netback: tx stalls with default credit_bytes

This situation happens when netif->credit_bytes is using the default of ~0UL,
effectively -1.  Once the current tx packet size is greater than the
netif->remaining_credit, transmits will stall until
netif->remaining_credit wraps back to ~0UL in tx_add_credit().  The
min(netif->remaining_credit + netif->credit_bytes, max_burst) has the
effect of decrementing netif->remaining_credit by 1.  The min will
continually be less than the current tx packet size until tx_add_credit() is
called packet size times which allows netif->remaining_credit to wrap back to
~0UL.

The patch splits the min() into two steps to eliminate the case of adding by -1.

signed-of-by Kirk Allan <kallan@novell.com>



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On 6/11/06 10:50 pm, "Kirk Allan" <kallan@novell.com> wrote:
> This situation happens when netif->credit_bytes is using the default of
~0UL,
> effectively -1.  Once the current tx packet size is greater than the
> netif->remaining_credit, transmits will stall until
netif->remaining_credit
> wraps back to ~0UL in tx_add_credit().  The min(netif->remaining_credit
+
> netif->credit_bytes, max_burst) has the effect of decrementing
> netif->remaining_credit by 1.  The min will continually be less than the
> current tx packet size until tx_add_credit() is called packet size times
which
> allows netif->remaining_credit to wrap back to ~0UL.
> 
> The patch splits the min() into two steps to eliminate the case of adding
by
> -1.
Nice catch. Thanks.

 -- Keir



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