.\" $OpenBSD: counters_alloc.9,v 1.13 2023/09/16 09:33:28 mpi Exp $ .\" .\" Copyright (c) 2016 David Gwynne .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .Dd $Mdocdate: September 16 2023 $ .Dt COUNTERS_ALLOC 9 .Os .Sh NAME .Nm counters_alloc , .Nm counters_free , .Nm COUNTERS_BOOT_MEMORY , .Nm COUNTERS_BOOT_INITIALIZER , .Nm counters_alloc_ncpus , .Nm counters_enter , .Nm counters_leave , .Nm counters_inc , .Nm counters_add , .Nm counters_pkt , .Nm counters_read , .Nm counters_zero .Nd per CPU counters .Sh SYNOPSIS .In sys/percpu.h .Ft struct cpumem * .Fn counters_alloc "unsigned int ncounters" .Ft void .Fn counters_free "struct cpumem *cm" "unsigned int ncounters" .Fn COUNTERS_BOOT_MEMORY "NAME" "unsigned int ncounters" .Fn COUNTERS_BOOT_INITIALIZER "NAME" .Ft struct cpumemt * .Fo counters_alloc_ncpus .Fa "struct cpumem *cm" .Fa "unsigned int ncounters" .Fc .Ft uint64_t * .Fn counters_enter "struct counters_ref *ref" "struct cpumem *cm" .Ft void .Fn counters_leave "struct counters_ref *ref" "struct cpumem *cm" .Ft void .Fn counters_inc "struct cpumem *cm" "unsigned int counter" .Ft void .Fn counters_add "struct cpumem *cm" "unsigned int counter" "uint64_t v" .Ft void .Fo counters_pkt .Fa "struct cpumem *cm" .Fa "unsigned int pcounter" .Fa "unsigned int bcounter" .Fa "uint64_t bytes" .Fc .Ft void .Fo counters_read .Fa "struct cpumem *cm" .Fa "uint64_t *counters" .Fa "unsigned int ncounters" .Fa "uint64_t *scratch" .Fc .Ft void .Fn counters_zero "struct cpumem *cm" "unsigned int ncounters" .Sh DESCRIPTION The per CPU counter API builds on the per CPU memory API and provides access to a series of uint64_t counter values on each CPU. .Pp The API provides versioning of counter updates without using interlocked CPU instructions so they can all be read in a consistent state. Updates to counters should be limited to addition or subtraction of uint64_t values. .Pp An alternate implementation of the API is provided on uni-processor systems (i.e. when the kernel is not built with .Dv MULTIPROCESSOR defined) that provides no overhead compared to direct access to a data structure. This allows the API to be used without affecting the performance of uni-processor systems. .Pp .Fn counters_alloc allocates memory for a series of uint64_t values on each CPU. .Fa ncounters specifies the number of counters to be allocated. The counters will be zeroed on allocation. .Pp .Fn counters_free deallocates each CPU's counters. The same .Fa ncounters argument originally provided to .Fn counters_alloc must be passed to .Fn counters_free . .Pp .Fn counters_alloc may only be used after all the CPUs in the system have been attached. If a set of CPU counters needs to be available during early boot, a cpumem pointer and counters for the boot CPU may be statically allocated. .Pp .Fn COUNTERS_BOOT_MEMORY statically allocates a set of counter for use on the boot CPU before the other CPUs in the system have been attached. The allocation is identified by .Fa NAME and provides memory for the number of counters specified by .Fa ncounters . The counters will be initialised to zero. .Pp .Fn COUNTERS_BOOT_INITIALIZER is used to initialise a cpumem pointer with the memory that was previously allocated using .Fn COUNTERS_BOOT_MEMORY and identified by .Fa NAME . .Pp .Fn counters_alloc_ncpus allocates additional sets of counters for the CPUs that were attached during boot. The cpumem structure .Fa cm must have been initialised with .Fn COUNTERS_BOOT_INITIALIZER . The same number of counters originally passed to .Fa COUNTERS_BOOT_MEMORY must be specified by .Fa ncounters . The counters on the boot CPU will be preserved, while the counters for the additional CPUs will be zeroed on allocation. .Pp Counters that have been allocated with .Fn COUNTERS_BOOT_MEMORY and .Fn counters_alloc_ncpus cannot be deallocated with .Fa counters_free . .Pp .Fn counters_enter provides access to the current CPU's set of counters referenced by .Fa cm . The caller's reference to the counters is held by .Fa ref . .Pp .Fn counters_leave indicates the end of access to the current CPU's set of counters referenced by .Fa cm . The reference held by .Fa ref is released by this call. .Pp .Fn counters_inc increments the counter at the index specified by .Fa counter in the array of counters referenced by .Fa cm . .Pp .Fn counters_add adds the value of .Fa v to the counter at the index specified by .Fa counter in the array of counters referenced by .Fa cm . .Pp .Fn counters_pkt increments the value at the index specified by .Fa pcounter and adds the value of .Fa bytes to the counter at the index specified by .Fa bcounter in the array of counters referenced by .Fa cm . .Pp .Fn counters_read iterates over each CPU's set of counters referenced by .Fa cm , takes a consistent snapshot of the counters, and then sums them together. The sum of the counters is written to the .Fa counters array. The number of counters is specified with .Fa ncounters . .Fa scratch may point to a buffer used to temporarily hold .Fa counters . If .Dv NULL , one will be dynamically allocated and freed. .Pp .Fn counters_zero iterates over each CPU's set of counters referenced by .Fa cm and zeroes them. The number of counters is specified with .Fa ncounters . .Fn counters_zero itself does not prevent concurrent updates of the counters; it is up to the caller to serialise this call with other actions. .Sh CONTEXT .Fn counters_alloc , .Fn counters_free , .Fn counters_alloc_ncpus , and .Fn counters_read may be called during autoconf, or from process context. .Pp .Fn counters_enter , .Fn counters_leave , .Fn counters_inc , .Fn counters_add , .Fn counters_pkt , and .Fn counters_zero may be called during autoconf, from process context, or from interrupt context. The per CPU counters API does not provide any locking or serialisation of access to each CPU's set of counters beyond isolating each CPU's update. It is up to the caller to provide appropriate locking or serialisation around calls to these functions to prevent concurrent access to the relevant data structures. .Sh RETURN VALUES .Fn counters_alloc and .Fn counters_alloc_ncpus will return an opaque cpumem pointer that references each CPU's set of counters. .Pp .Fn counters_enter returns a reference to the current CPU's set of counters. .Sh EXAMPLES The following is an example of providing per CPU counters at boot time based on the .Xr mbuf 9 statistics code in .Pa sys/kern/uipc_mbuf.c . .Bd -literal /* mbuf stats */ COUNTERS_BOOT_MEMORY(mbstat_boot, MBSTAT_COUNT); struct cpumem *mbstat = COUNTERS_BOOT_INITIALIZER(mbstat_boot); /* * this function is called from init_main.c after devices * (including additional CPUs) have been attached */ void mbcpuinit() { mbstat = counters_alloc_ncpus(mbstat, MBSTAT_COUNT); } struct mbuf * m_get(int nowait, int type) { ... struct counters_ref cr; uint64_t *counters; int s; ... s = splnet(); counters = counters_enter(&cr, mbstat); counters[type]++; counters_leave(&cr, mbstat); splx(s); ... } struct mbuf * m_free(struct mbuf *m) { ... struct counters_ref cr; uint64_t *counters; int s; ... s = splnet(); counters = counters_enter(&cr, mbstat); counters[m->m_type]--; counters_leave(&cr, mbstat); splx(s); ... } .Ed .Sh SEE ALSO .Xr cpumem_get 9 , .Xr malloc 9 .Sh HISTORY The per CPU counter API first appeared in .Ox 6.1 . .Sh AUTHORS The per CPU counter API was written by .An David Gwynne Aq Mt dlg@openbsd.org .