Inside a virtual machine, writing the RX ring tail pointer may incur a
substantial overhead of processing inside the hypervisor. Minimise
this overhead by writing the tail pointer once per batch of
descriptors, rather than once per descriptor.
Profiling under qemu-kvm (version 1.6.2) shows that this reduces the
amount of time taken to refill the RX descriptor ring by around 90%.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Operations which are negligible on physical hardware (such as issuing
a posted write to the transmit ring tail register) may involve
substantial amounts of processing within the hypervisor if running in
a virtual machine.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
It is unclear from the datasheets whether or not the TX ring can be
completely filled (i.e. whether writing the tail value as equal to the
current head value will cause the ring to be treated as completely
full or completely empty). It is very plausible that this edge case
could differ in behaviour between real hardware and the many
implementations of an emulated Intel NIC found in various virtual
machines. Err on the side of caution and always leave at least one
ring entry empty.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The Intel 10 Gigabit NICs have a datapath that is almost
register-compatible with the Intel 1 Gigabit NICs. Expose common
functionality to avoid duplication of code in the new "intelx" driver.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The Intel 10 Gigabit NICs use the same simplified (aka "legacy")
descriptor format and the same layout for descriptor register blocks
as the Intel 1 Gigabit NICs. The offsets of the descriptor register
blocks are not the same.
Simplify reuse of the existing code by removing all hardcoded offsets
for registers within descriptor register blocks, and ensuring that all
offsets are calculated using the descriptor register block base
address provided via intel_init_ring().
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The Intel NIC emulation in some versions of VMware seems to suffer
from a flaw whereby the Interrupt Cause Register (ICR) fails to assert
the usual "packet received" bit (ICR.RXT0) if a receive overflow
(ICR.RXO) has also occurred.
Work around this flaw by polling for completed descriptors whenever
either ICR.RXT0 or ICR.RXO is asserted.
Reported-by: Miroslav Halas <miroslav.halas@bankofamerica.com>
Debugged-by: Miroslav Halas <miroslav.halas@bankofamerica.com>
Tested-by: Miroslav Halas <miroslav.halas@bankofamerica.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
On i350 the datasheet contradicts itself in stating that the default
value of RXDCTL.ENABLE for queue zero is both set (according to the
"Receive Initialization" section) and unset (according to the "Receive
Descriptor Control - RXDCTL" section). Empirical evidence suggests
that the default value is unset.
Explicitly enable both transmit and receive queues to avoid any
ambiguity.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
On 82576 (and probably others), the datasheet states that "the tail
register of the queue (RDT[n]) should not be bumped until the queue is
enabled". There is some confusion over exactly what constitutes
"enabled": the initialisation blurb says that we should "poll the
RXDCTL register until the ENABLE bit is set", while the description
for the RXDCTL register says that the ENABLE bit is set by default
(for queue zero). Empirical evidence suggests that the ENABLE bit
reads as set immediately after writing to RCTL.EN, and so polling is
not necessary.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
