cc412412db
2 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Robert Watson
|
7527624efa |
Several years after initial development, merge prototype support for
linking NIC Receive Side Scaling (RSS) to the network stack's
connection-group implementation. This prototype (and derived patches)
are in use at Juniper and several other FreeBSD-using companies, so
despite some reservations about its maturity, merge the patch to the
base tree so that it can be iteratively refined in collaboration rather
than maintained as a set of gradually diverging patch sets.
(1) Merge a software implementation of the Toeplitz hash specified in
RSS implemented by David Malone. This is used to allow suitable
pcbgroup placement of connections before the first packet is
received from the NIC. Software hashing is generally avoided,
however, due to high cost of the hash on general-purpose CPUs.
(2) In in_rss.c, maintain authoritative versions of RSS state intended
to be pushed to each NIC, including keying material, hash
algorithm/ configuration, and buckets. Provide software-facing
interfaces to hash 2- and 4-tuples for IPv4 and IPv6 using both
the RSS standardised Toeplitz and a 'naive' variation with a hash
efficient in software but with poor distribution properties.
Implement rss_m2cpuid()to be used by netisr and other load
balancing code to look up the CPU on which an mbuf should be
processed.
(3) In the Ethernet link layer, allow netisr distribution using RSS as
a source of policy as an alternative to source ordering; continue
to default to direct dispatch (i.e., don't try and requeue packets
for processing on the 'right' CPU if they arrive in a directly
dispatchable context).
(4) Allow RSS to control tuning of connection groups in order to align
groups with RSS buckets. If a packet arrives on a protocol using
connection groups, and contains a suitable hardware-generated
hash, use that hash value to select the connection group for pcb
lookup for both IPv4 and IPv6. If no hardware-generated Toeplitz
hash is available, we fall back on regular PCB lookup risking
contention rather than pay the cost of Toeplitz in software --
this is a less scalable but, at my last measurement, faster
approach. As core counts go up, we may want to revise this
strategy despite CPU overhead.
Where device drivers suitably configure NICs, and connection groups /
RSS are enabled, this should avoid both lock and line contention during
connection lookup for TCP. This commit does not modify any device
drivers to tune device RSS configuration to the global RSS
configuration; patches are in circulation to do this for at least
Chelsio T3 and Intel 1G/10G drivers. Currently, the KPI for device
drivers is not particularly robust, nor aware of more advanced features
such as runtime reconfiguration/rebalancing. This will hopefully prove
a useful starting point for refinement.
No MFC is scheduled as we will first want to nail down a more mature
and maintainable KPI/KBI for device drivers.
Sponsored by: Juniper Networks (original work)
Sponsored by: EMC/Isilon (patch update and merge)
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Robert Watson
|
52cd27cb58 |
Implement a CPU-affine TCP and UDP connection lookup data structure,
struct inpcbgroup. pcbgroups, or "connection groups", supplement the existing inpcbinfo connection hash table, which when pcbgroups are enabled, might now be thought of more usefully as a per-protocol 4-tuple reservation table. Connections are assigned to connection groups base on a hash of their 4-tuple; wildcard sockets require special handling, and are members of all connection groups. During a connection lookup, a per-connection group lock is employed rather than the global pcbinfo lock. By aligning connection groups with input path processing, connection groups take on an effective CPU affinity, especially when aligned with RSS work placement (see a forthcoming commit for details). This eliminates cache line migration associated with global, protocol-layer data structures in steady state TCP and UDP processing (with the exception of protocol-layer statistics; further commit to follow). Elements of this approach were inspired by Willman, Rixner, and Cox's 2006 USENIX paper, "An Evaluation of Network Stack Parallelization Strategies in Modern Operating Systems". However, there are also significant differences: we maintain the inpcb lock, rather than using the connection group lock for per-connection state. Likewise, the focus of this implementation is alignment with NIC packet distribution strategies such as RSS, rather than pure software strategies. Despite that focus, software distribution is supported through the parallel netisr implementation, and works well in configurations where the number of hardware threads is greater than the number of NIC input queues, such as in the RMI XLR threaded MIPS architecture. Another important difference is the continued maintenance of existing hash tables as "reservation tables" -- these are useful both to distinguish the resource allocation aspect of protocol name management and the more common-case lookup aspect. In configurations where connection tables are aligned with hardware hashes, it is desirable to use the traditional lookup tables for loopback or encapsulated traffic rather than take the expense of hardware hashes that are hard to implement efficiently in software (such as RSS Toeplitz). Connection group support is enabled by compiling "options PCBGROUP" into your kernel configuration; for the time being, this is an experimental feature, and hence is not enabled by default. Subject to the limited MFCability of change dependencies in inpcb, and its change to the inpcbinfo init function signature, this change in principle could be merged to FreeBSD 8.x. Reviewed by: bz Sponsored by: Juniper Networks, Inc. |