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perf sched replay: Alloc the memory of pid_to_task dynamically to adapt to the unexpected change of pid_max
The current memory allocation of struct task_desc *pid_to_task[MAX_PID] is in a permanent and preset way, and it has two problems: Problem 1: If the pid_max, which is the max number of pids in the system, is much smaller than MAX_PID (1024*1000), then it causes a waste of stack memory. This may happen in the case where the number of cpu cores is much smaller than 1000. Problem 2: If the pid_max is changed from the default value to a value larger than MAX_PID, then it will cause assertion failure problem. The maximum value of pid_max can be set to pid_max_max (see pidmap_init defined in kernel/pid.c), which equals to PID_MAX_LIMIT. In x86_64, PID_MAX_LIMIT is 4*1024*1024 (defined in include/linux/threads.h). This value is much larger than MAX_PID, and will take up 32768 Kbytes (4*1024*1024*8/1024) for memory allocation of pid_to_task, which is much larger than the default 8192 Kbytes of the stack size of calling process. Due to these two problems, we use calloc to allocate the memory of pid_to_task dynamically. Example: Test environment: x86_64 with 160 cores $ cat /proc/sys/kernel/pid_max 163840 $ echo 1025000 > /proc/sys/kernel/pid_max $ cat /proc/sys/kernel/pid_max 1025000 Run some applications until the pid of some process is greater than the value of MAX_PID (1024*1000). Before this patch: $ perf sched replay run measurement overhead: 221 nsecs sleep measurement overhead: 55480 nsecs the run test took 1000008 nsecs the sleep test took 1063151 nsecs perf: builtin-sched.c:330: register_pid: Assertion `!(pid >= 1024000)' failed. Aborted After this patch: $ perf sched replay run measurement overhead: 221 nsecs sleep measurement overhead: 55435 nsecs the run test took 1000004 nsecs the sleep test took 1059312 nsecs nr_run_events: 10 nr_sleep_events: 1562 nr_wakeup_events: 5 task 0 ( :1: 1), nr_events: 1 task 1 ( :2: 2), nr_events: 1 task 2 ( :3: 3), nr_events: 1 task 3 ( :5: 5), nr_events: 1 ... Signed-off-by: Yunlong Song <yunlong.song@huawei.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Wang Nan <wangnan0@huawei.com> Link: http://lkml.kernel.org/r/1427809596-29559-4-git-send-email-yunlong.song@huawei.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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1 changed files with 9 additions and 2 deletions
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@ -23,6 +23,7 @@
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#include <semaphore.h>
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#include <pthread.h>
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#include <math.h>
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#include <api/fs/fs.h>
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#define PR_SET_NAME 15 /* Set process name */
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#define MAX_CPUS 4096
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@ -124,7 +125,7 @@ struct perf_sched {
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struct perf_tool tool;
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const char *sort_order;
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unsigned long nr_tasks;
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struct task_desc *pid_to_task[MAX_PID];
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struct task_desc **pid_to_task;
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struct task_desc **tasks;
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const struct trace_sched_handler *tp_handler;
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pthread_mutex_t start_work_mutex;
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@ -326,8 +327,14 @@ static struct task_desc *register_pid(struct perf_sched *sched,
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unsigned long pid, const char *comm)
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{
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struct task_desc *task;
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static int pid_max;
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BUG_ON(pid >= MAX_PID);
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if (sched->pid_to_task == NULL) {
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if (sysctl__read_int("kernel/pid_max", &pid_max) < 0)
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pid_max = MAX_PID;
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BUG_ON((sched->pid_to_task = calloc(pid_max, sizeof(struct task_desc *))) == NULL);
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}
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BUG_ON(pid >= (unsigned long)pid_max);
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task = sched->pid_to_task[pid];
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