Refine netisr.c comments a bit.
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rwatson
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d90c98559e
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0b860a6956
@ -32,13 +32,13 @@ __FBSDID("$FreeBSD$");
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* dispatched) and asynchronous (deferred dispatch) processing of packets by
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* registered protocol handlers. Callers pass a protocol identifier and
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* packet to netisr, along with a direct dispatch hint, and work will either
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* be immediately processed with the registered handler, or passed to a
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* kernel software interrupt (SWI) thread for deferred dispatch. Callers
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* will generally select one or the other based on:
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* be immediately processed by the registered handler, or passed to a
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* software interrupt (SWI) thread for deferred dispatch. Callers will
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* generally select one or the other based on:
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*
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* - Might directly dispatching a netisr handler lead to code reentrance or
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* - Whether directly dispatching a netisr handler lead to code reentrance or
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* lock recursion, such as entering the socket code from the socket code.
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* - Might directly dispatching a netisr handler lead to recursive
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* - Whether directly dispatching a netisr handler lead to recursive
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* processing, such as when decapsulating several wrapped layers of tunnel
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* information (IPSEC within IPSEC within ...).
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*
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@ -54,9 +54,9 @@ __FBSDID("$FreeBSD$");
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* more than one flow.
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*
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* netisr supports several policy variations, represented by the
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* NETISR_POLICY_* constants, allowing protocols to play a varying role in
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* NETISR_POLICY_* constants, allowing protocols to play various roles in
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* identifying flows, assigning work to CPUs, etc. These are described in
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* detail in netisr.h.
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* netisr.h.
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*/
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#include "opt_ddb.h"
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@ -101,7 +101,7 @@ __FBSDID("$FreeBSD$");
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*
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* Note: the NETISR_LOCKING define controls whether read locks are acquired
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* in packet processing paths requiring netisr registration stability. This
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* is disabled by default as it can lead to a measurable performance
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* is disabled by default as it can lead to measurable performance
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* degradation even with rmlocks (3%-6% for loopback ping-pong traffic), and
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* because netisr registration and unregistration is extremely rare at
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* runtime. If it becomes more common, this decision should be revisited.
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@ -166,8 +166,9 @@ SYSCTL_INT(_net_isr, OID_AUTO, bindthreads, CTLFLAG_RD,
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&netisr_bindthreads, 0, "Bind netisr threads to CPUs.");
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/*
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* Limit per-workstream queues to at most net.isr.maxqlimit, both for initial
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* configuration and later modification using netisr_setqlimit().
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* Limit per-workstream mbuf queue limits s to at most net.isr.maxqlimit,
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* both for initial configuration and later modification using
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* netisr_setqlimit().
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*/
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#define NETISR_DEFAULT_MAXQLIMIT 10240
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static u_int netisr_maxqlimit = NETISR_DEFAULT_MAXQLIMIT;
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@ -177,9 +178,9 @@ SYSCTL_INT(_net_isr, OID_AUTO, maxqlimit, CTLFLAG_RD,
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"Maximum netisr per-protocol, per-CPU queue depth.");
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/*
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* The default per-workstream queue limit for protocols that don't initialize
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* the nh_qlimit field of their struct netisr_handler. If this is set above
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* netisr_maxqlimit, we truncate it to the maximum during boot.
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* The default per-workstream mbuf queue limit for protocols that don't
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* initialize the nh_qlimit field of their struct netisr_handler. If this is
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* set above netisr_maxqlimit, we truncate it to the maximum during boot.
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*/
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#define NETISR_DEFAULT_DEFAULTQLIMIT 256
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static u_int netisr_defaultqlimit = NETISR_DEFAULT_DEFAULTQLIMIT;
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@ -237,12 +238,14 @@ struct netisr_work {
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};
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/*
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* Workstreams hold a set of ordered work across each protocol, and are
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* Workstreams hold a queue of ordered work across each protocol, and are
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* described by netisr_workstream. Each workstream is associated with a
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* worker thread, which in turn is pinned to a CPU. Work associated with a
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* workstream can be processd in other threads during direct dispatch;
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* concurrent processing is prevented by the NWS_RUNNING flag, which
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* indicates that a thread is already processing the work queue.
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* indicates that a thread is already processing the work queue. It is
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* important to prevent a directly dispatched packet from "skipping ahead" of
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* work already in the workstream queue.
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*/
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struct netisr_workstream {
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struct intr_event *nws_intr_event; /* Handler for stream. */
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@ -317,7 +320,7 @@ netisr_get_cpuid(u_int cpunumber)
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}
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/*
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* The default implementation of -> CPU ID mapping.
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* The default implementation of flow -> CPU ID mapping.
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*
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* Non-static so that protocols can use it to map their own work to specific
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* CPUs in a manner consistent to netisr for affinity purposes.
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@ -437,7 +440,7 @@ netisr_clearqdrops(const struct netisr_handler *nhp)
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}
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/*
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* Query the current drop counters across all workstreams for a protocol.
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* Query current drop counters across all workstreams for a protocol.
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*/
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void
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netisr_getqdrops(const struct netisr_handler *nhp, u_int64_t *qdropp)
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@ -472,7 +475,7 @@ netisr_getqdrops(const struct netisr_handler *nhp, u_int64_t *qdropp)
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}
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/*
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* Query the current queue limit for per-workstream queues for a protocol.
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* Query current per-workstream queue limit for a protocol.
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*/
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void
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netisr_getqlimit(const struct netisr_handler *nhp, u_int *qlimitp)
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@ -726,7 +729,7 @@ netisr_process_workstream_proto(struct netisr_workstream *nwsp, u_int proto)
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}
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/*
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* SWI handler for netisr -- processes prackets in a set of workstreams that
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* SWI handler for netisr -- processes packets in a set of workstreams that
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* it owns, woken up by calls to NWS_SIGNAL(). If this workstream is already
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* being direct dispatched, go back to sleep and wait for the dispatching
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* thread to wake us up again.
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@ -794,6 +797,11 @@ netisr_queue_workstream(struct netisr_workstream *nwsp, u_int proto,
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npwp->nw_len++;
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if (npwp->nw_len > npwp->nw_watermark)
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npwp->nw_watermark = npwp->nw_len;
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/*
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* We must set the bit regardless of NWS_RUNNING, so that
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* swi_net() keeps calling netisr_process_workstream_proto().
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*/
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nwsp->nws_pendingbits |= (1 << proto);
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if (!(nwsp->nws_flags &
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(NWS_RUNNING | NWS_DISPATCHING | NWS_SCHEDULED))) {
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@ -874,7 +882,7 @@ netisr_queue(u_int proto, struct mbuf *m)
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}
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/*
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* Dispatch a packet for netisr processing, direct dispatch permitted by
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* Dispatch a packet for netisr processing; direct dispatch is permitted by
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* calling context.
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*/
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int
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