"basic_percpu_ops_test" is a slightly more "realistic" variant, implementing a few simple per-cpu operations and testing their correctness.

Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com CC: Shuah Khan shuahkh@osg.samsung.com CC: Russell King linux@arm.linux.org.uk CC: Catalin Marinas catalin.marinas@arm.com CC: Will Deacon will.deacon@arm.com CC: Thomas Gleixner tglx@linutronix.de CC: Paul Turner pjt@google.com CC: Andrew Hunter ahh@google.com CC: Peter Zijlstra peterz@infradead.org CC: Andy Lutomirski luto@amacapital.net CC: Andi Kleen andi@firstfloor.org CC: Dave Watson davejwatson@fb.com CC: Chris Lameter cl@linux.com CC: Ingo Molnar mingo@redhat.com CC: "H. Peter Anvin" hpa@zytor.com CC: Ben Maurer bmaurer@fb.com CC: Steven Rostedt rostedt@goodmis.org CC: "Paul E. McKenney" paulmck@linux.vnet.ibm.com CC: Josh Triplett josh@joshtriplett.org CC: Linus Torvalds torvalds@linux-foundation.org CC: Andrew Morton akpm@linux-foundation.org CC: Boqun Feng boqun.feng@gmail.com CC: linux-kselftest@vger.kernel.org CC: linux-api@vger.kernel.org --- Changes since v1: - Use only rseq, remove use of cpu_opv system call. --- .../testing/selftests/rseq/basic_percpu_ops_test.c | 313 +++++++++++++++++++++ 1 file changed, 313 insertions(+) create mode 100644 tools/testing/selftests/rseq/basic_percpu_ops_test.c

diff --git a/tools/testing/selftests/rseq/basic_percpu_ops_test.c b/tools/testing/selftests/rseq/basic_percpu_ops_test.c new file mode 100644 index 000000000000..96ef27905879 --- /dev/null +++ b/tools/testing/selftests/rseq/basic_percpu_ops_test.c @@ -0,0 +1,313 @@ +// SPDX-License-Identifier: LGPL-2.1 +#define _GNU_SOURCE +#include <assert.h> +#include <pthread.h> +#include <sched.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <stddef.h> + +#include "rseq.h" + +#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0])) + +struct percpu_lock_entry { + intptr_t v; +} __attribute__((aligned(128))); + +struct percpu_lock { + struct percpu_lock_entry c[CPU_SETSIZE]; +}; + +struct test_data_entry { + intptr_t count; +} __attribute__((aligned(128))); + +struct spinlock_test_data { + struct percpu_lock lock; + struct test_data_entry c[CPU_SETSIZE]; + int reps; +}; + +struct percpu_list_node { + intptr_t data; + struct percpu_list_node *next; +}; + +struct percpu_list_entry { + struct percpu_list_node *head; +} __attribute__((aligned(128))); + +struct percpu_list { + struct percpu_list_entry c[CPU_SETSIZE]; +}; + +/* A simple percpu spinlock. Returns the cpu lock was acquired on. */ +int rseq_this_cpu_lock(struct percpu_lock *lock) +{ + int cpu; + + for (;;) { + int ret; + + cpu = rseq_cpu_start(); + ret = rseq_cmpeqv_storev(&lock->c[cpu].v, + 0, 1, cpu); + if (rseq_likely(!ret)) + break; + /* Retry if comparison fails or rseq aborts. */ + } + /* + * Acquire semantic when taking lock after control dependency. + * Matches rseq_smp_store_release(). + */ + rseq_smp_acquire__after_ctrl_dep(); + return cpu; +} + +void rseq_percpu_unlock(struct percpu_lock *lock, int cpu) +{ + assert(lock->c[cpu].v == 1); + /* + * Release lock, with release semantic. Matches + * rseq_smp_acquire__after_ctrl_dep(). + */ + rseq_smp_store_release(&lock->c[cpu].v, 0); +} + +void *test_percpu_spinlock_thread(void *arg) +{ + struct spinlock_test_data *data = arg; + int i, cpu; + + if (rseq_register_current_thread()) { + fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n", + errno, strerror(errno)); + abort(); + } + for (i = 0; i < data->reps; i++) { + cpu = rseq_this_cpu_lock(&data->lock); + data->c[cpu].count++; + rseq_percpu_unlock(&data->lock, cpu); + } + if (rseq_unregister_current_thread()) { + fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n", + errno, strerror(errno)); + abort(); + } + + return NULL; +} + +/* + * A simple test which implements a sharded counter using a per-cpu + * lock. Obviously real applications might prefer to simply use a + * per-cpu increment; however, this is reasonable for a test and the + * lock can be extended to synchronize more complicated operations. + */ +void test_percpu_spinlock(void) +{ + const int num_threads = 200; + int i; + uint64_t sum; + pthread_t test_threads[num_threads]; + struct spinlock_test_data data; + + memset(&data, 0, sizeof(data)); + data.reps = 5000; + + for (i = 0; i < num_threads; i++) + pthread_create(&test_threads[i], NULL, + test_percpu_spinlock_thread, &data); + + for (i = 0; i < num_threads; i++) + pthread_join(test_threads[i], NULL); + + sum = 0; + for (i = 0; i < CPU_SETSIZE; i++) + sum += data.c[i].count; + + assert(sum == (uint64_t)data.reps * num_threads); +} + +void this_cpu_list_push(struct percpu_list *list, + struct percpu_list_node *node, + int *_cpu) +{ + int cpu; + + for (;;) { + intptr_t *targetptr, newval, expect; + int ret; + + cpu = rseq_cpu_start(); + /* Load list->c[cpu].head with single-copy atomicity. */ + expect = (intptr_t)RSEQ_READ_ONCE(list->c[cpu].head); + newval = (intptr_t)node; + targetptr = (intptr_t *)&list->c[cpu].head; + node->next = (struct percpu_list_node *)expect; + ret = rseq_cmpeqv_storev(targetptr, expect, newval, cpu); + if (rseq_likely(!ret)) + break; + /* Retry if comparison fails or rseq aborts. */ + } + if (_cpu) + *_cpu = cpu; +} + +/* + * Unlike a traditional lock-less linked list; the availability of a + * rseq primitive allows us to implement pop without concerns over + * ABA-type races. + */ +struct percpu_list_node *this_cpu_list_pop(struct percpu_list *list, + int *_cpu) +{ + for (;;) { + struct percpu_list_node *head; + intptr_t *targetptr, expectnot, *load; + off_t offset; + int ret, cpu; + + cpu = rseq_cpu_start(); + targetptr = (intptr_t *)&list->c[cpu].head; + expectnot = (intptr_t)NULL; + offset = offsetof(struct percpu_list_node, next); + load = (intptr_t *)&head; + ret = rseq_cmpnev_storeoffp_load(targetptr, expectnot, + offset, load, cpu); + if (rseq_likely(!ret)) { + if (_cpu) + *_cpu = cpu; + return head; + } + if (ret > 0) + return NULL; + /* Retry if rseq aborts. */ + } +} + +/* + * __percpu_list_pop is not safe against concurrent accesses. Should + * only be used on lists that are not concurrently modified. + */ +struct percpu_list_node *__percpu_list_pop(struct percpu_list *list, int cpu) +{ + struct percpu_list_node *node; + + node = list->c[cpu].head; + if (!node) + return NULL; + list->c[cpu].head = node->next; + return node; +} + +void *test_percpu_list_thread(void *arg) +{ + int i; + struct percpu_list *list = (struct percpu_list *)arg; + + if (rseq_register_current_thread()) { + fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n", + errno, strerror(errno)); + abort(); + } + + for (i = 0; i < 100000; i++) { + struct percpu_list_node *node; + + node = this_cpu_list_pop(list, NULL); + sched_yield(); /* encourage shuffling */ + if (node) + this_cpu_list_push(list, node, NULL); + } + + if (rseq_unregister_current_thread()) { + fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n", + errno, strerror(errno)); + abort(); + } + + return NULL; +} + +/* Simultaneous modification to a per-cpu linked list from many threads. */ +void test_percpu_list(void) +{ + int i, j; + uint64_t sum = 0, expected_sum = 0; + struct percpu_list list; + pthread_t test_threads[200]; + cpu_set_t allowed_cpus; + + memset(&list, 0, sizeof(list)); + + /* Generate list entries for every usable cpu. */ + sched_getaffinity(0, sizeof(allowed_cpus), &allowed_cpus); + for (i = 0; i < CPU_SETSIZE; i++) { + if (!CPU_ISSET(i, &allowed_cpus)) + continue; + for (j = 1; j <= 100; j++) { + struct percpu_list_node *node; + + expected_sum += j; + + node = malloc(sizeof(*node)); + assert(node); + node->data = j; + node->next = list.c[i].head; + list.c[i].head = node; + } + } + + for (i = 0; i < 200; i++) + pthread_create(&test_threads[i], NULL, + test_percpu_list_thread, &list); + + for (i = 0; i < 200; i++) + pthread_join(test_threads[i], NULL); + + for (i = 0; i < CPU_SETSIZE; i++) { + struct percpu_list_node *node; + + if (!CPU_ISSET(i, &allowed_cpus)) + continue; + + while ((node = __percpu_list_pop(&list, i))) { + sum += node->data; + free(node); + } + } + + /* + * All entries should now be accounted for (unless some external + * actor is interfering with our allowed affinity while this + * test is running). + */ + assert(sum == expected_sum); +} + +int main(int argc, char **argv) +{ + if (rseq_register_current_thread()) { + fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n", + errno, strerror(errno)); + goto error; + } + printf("spinlock\n"); + test_percpu_spinlock(); + printf("percpu_list\n"); + test_percpu_list(); + if (rseq_unregister_current_thread()) { + fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n", + errno, strerror(errno)); + goto error; + } + return 0; + +error: + return -1; +} +