will cause the network stack to operate without the Giant lock by
default. This change has the potential to improve performance by
increasing parallelism and decreasing latency in network processing.
Due to the potential exposure of existing or new bugs, the following
compatibility functionality is maintained:
- It is still possible to disable Giant-free operation by setting
debug.mpsafenet to 0 in loader.conf.
- Add "options NET_WITH_GIANT", which will restore the default value of
debug.mpsafenet to 0, and is intended for use on systems compiled with
known unsafe components, or where a more conservative configuration is
desired.
- Add a new declaration, NET_NEEDS_GIANT("componentname"), which permits
kernel components to declare dependence on Giant over the network
stack. If the declaration is made by a preloaded module or a compiled
in component, the disposition of debug.mpsafenet will be set to 0 and
a warning concerning performance degraded operation printed to the
console. If it is declared by a loadable kernel module after boot, a
warning is displayed but the disposition cannot be changed. This is
implemented by defining a new SYSINIT() value, SI_SUB_SETTINGS, which
is intended for the processing of configuration choices after tunables
are read in and the console is available to generate errors, but
before much else gets going.
This compatibility behavior will go away when we've finished the last
of the locking work and are confident that operation is correct.
its users.
netisr_queue() now returns (0) on success and ERRNO on failure. At the
moment ENXIO (netisr queue not functional) and ENOBUFS (netisr queue full)
are supported.
Previously it would return (1) on success but the return value of IF_HANDOFF()
was interpreted wrongly and (0) was actually returned on success. Due to this
schednetisr() was never called to kick the scheduling of the isr. However this
was masked by other normal packets coming through netisr_dispatch() causing the
dequeueing of waiting packets.
PR: kern/70988
Found by: MOROHOSHI Akihiko <moro@remus.dti.ne.jp>
MFC after: 3 days
whether or not the isr needs to hold Giant when running; Giant-less
operation is also controlled by the setting of debug_mpsafenet
o mark all netisr's except NETISR_IP as needing Giant
o add a GIANT_REQUIRED assertion to the top of netisr's that need Giant
o pickup Giant (when debug_mpsafenet is 1) inside ip_input before
calling up with a packet
o change netisr handling so swi_net runs w/o Giant; instead we grab
Giant before invoking handlers based on whether the handler needs Giant
o change netisr handling so that netisr's that are marked MPSAFE may
have multiple instances active at a time
o add netisr statistics for packets dropped because the isr is inactive
Supported by: FreeBSD Foundation
o move it from subr_bus.c to netisr.c where it more properly belongs
o add NET_PICKUP_GIANT and NET_DROP_GIANT macros that will be used to
grab Giant as needed when MPSAFE operation is enabled
Supported by: FreeBSD Foundation
any queued packets for the isr, process those packets before the newly
submitted packet, maintaining ordering of all packets being delivered
to the netisr. Remove the bypass counter since we don't bypass anymore.
Leave the comment about possible problems and options since later
performance optimization may change the strategy for addressing ordering
problems here.
Specifically, this maintains the strong isr ordering guarantee; additional
parallelism and lower latency may be possible by moving to weaker
guarantees (per-interface, for example). We will probably at some point
also want to remove the one instance netisr dispatch limit currently
enforced by a mutex, but it's not clear that's 100% safe yet, even in
the netperf branch.
Reviewed by: sam, others
(direct dispatch) in interrupt threads when the netisr in question
isn't already active. If a netisr is already active, or direct
dispatch is already in progress, we queue the packet for later
delivery. Previously, this option was disabled by default. I have
measured 20%+ performance improvements in IP packet forwarding with
this enabled.
Please report any problems ASAP, especially relating to stack depth or
out-of-order packet processing.
Discussed with: jlemon, peter
Sponsored by: DARPA, Network Associates Laboratories
drain routines are done by swi_net, which allows for better queue control
at some future point. Packets may also be directly dispatched to a netisr
instead of queued, this may be of interest at some installations, but
currently defaults to off.
Reviewed by: hsu, silby, jayanth, sam
Sponsored by: DARPA, NAI Labs
