On 2/24/2021 11:18 AM, Ciara Loftus wrote:
This commit introduces support for preferred busy polling
to the AF_XDP PMD. This feature aims to improve single-core
performance for AF_XDP sockets under heavy load.
A new vdev arg is introduced called 'busy_budget' whose default
value is 64. busy_budget is the value supplied to the kernel
with the SO_BUSY_POLL_BUDGET socket option and represents the
busy-polling NAPI budget. To set the budget to a different value
eg. 256:
--vdev=net_af_xdp0,iface=eth0,busy_budget=256
Preferred busy polling is enabled by default provided a kernel with
version >= v5.11 is in use. To disable it, set the budget to zero.
The following settings are also strongly recommended to be used in
conjunction with this feature:
echo 2 | sudo tee /sys/class/net/eth0/napi_defer_hard_irqs
echo 200000 | sudo tee /sys/class/net/eth0/gro_flush_timeout
.. where eth0 is the interface being used by the PMD.
Signed-off-by: Ciara Loftus <ciara.lof...@intel.com>
---
doc/guides/nics/af_xdp.rst | 38 ++++++++++++-
drivers/net/af_xdp/compat.h | 13 +++++
drivers/net/af_xdp/rte_eth_af_xdp.c | 85 ++++++++++++++++++++++++-----
3 files changed, 121 insertions(+), 15 deletions(-)
Can you please update the release notes too to announce the feature?
<...>
@@ -39,3 +39,16 @@ create_shared_socket(struct xsk_socket **xsk_ptr
__rte_unused,
return -1;
}
#endif
+
+#ifdef XDP_USE_NEED_WAKEUP
+static int
+syscall_needed(struct xsk_ring_prod *q, uint32_t busy_budget)
+{
+ return xsk_ring_prod__needs_wakeup(q) | busy_budget;
+}
+#else
+syscall_needed(struct xsk_ring_prod *q __rte_unused, uint32_t busy_budget)
+{
+ return busy_budget;
+}
Is the return type missing in the definition?
Also for the case when both 'XDP_USE_NEED_WAKEUP' & 'SO_PREFER_BUSY_POLL' this
function will always return '0', but current implementation doesn't know this in
the compile time and compiler can't optimize for it, do you think does it make
sense to do this optimization?
<...>
@@ -1628,8 +1670,22 @@ rte_pmd_af_xdp_probe(struct rte_vdev_device *dev)
return -EINVAL;
}
+#ifdef SO_PREFER_BUSY_POLL
+ busy_budget = busy_budget == -1 ? ETH_AF_XDP_DFLT_BUSY_BUDGET :
+ busy_budget;
+ if (!busy_budget)
+ AF_XDP_LOG(ERR, "Preferred busy polling disabled\n");
Is this an error case? What do you think changing the log level to DEBUG or
INFO?
Also how these compile time flags will work if the compiled environment and run
environment kernel version are different and incompatible?
Overall can it be possible to detect the support on runtime via 'setsockopt()'
without compile time macros and eliminate the compile time flags? Does it make
sense?
