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8af088710d
Ben Nagy reported a scalability problem with KVM/QEMU that hit very hard a single spinlock (idr_lock) in posix-timers code, on its 48 core machine. Even on a 16 cpu machine (2x4x2), a single test can show 98% of cpu time used in ticket_spin_lock, from lock_timer Ref: http://www.spinics.net/lists/kvm/msg51526.html Switching to RCU is quite easy, IDR being already RCU ready. idr_lock should be locked only for an insert/delete, not a lookup. Benchmark on a 2x4x2 machine, 16 processes calling timer_gettime(). Before : real 1m18.669s user 0m1.346s sys 1m17.180s After : real 0m3.296s user 0m1.366s sys 0m1.926s Reported-by: Ben Nagy <ben@iagu.net> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Tested-by: Ben Nagy <ben@iagu.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Avi Kivity <avi@redhat.com> Cc: John Stultz <johnstul@us.ibm.com> Cc: Richard Cochran <richard.cochran@omicron.at> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
130 lines
4.0 KiB
C
130 lines
4.0 KiB
C
#ifndef _linux_POSIX_TIMERS_H
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#define _linux_POSIX_TIMERS_H
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#include <linux/spinlock.h>
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#include <linux/list.h>
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#include <linux/sched.h>
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#include <linux/timex.h>
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#include <linux/alarmtimer.h>
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union cpu_time_count {
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cputime_t cpu;
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unsigned long long sched;
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};
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struct cpu_timer_list {
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struct list_head entry;
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union cpu_time_count expires, incr;
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struct task_struct *task;
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int firing;
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};
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/*
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* Bit fields within a clockid:
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*
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* The most significant 29 bits hold either a pid or a file descriptor.
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*
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* Bit 2 indicates whether a cpu clock refers to a thread or a process.
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*
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* Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
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*
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* A clockid is invalid if bits 2, 1, and 0 are all set.
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*/
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#define CPUCLOCK_PID(clock) ((pid_t) ~((clock) >> 3))
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#define CPUCLOCK_PERTHREAD(clock) \
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(((clock) & (clockid_t) CPUCLOCK_PERTHREAD_MASK) != 0)
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#define CPUCLOCK_PERTHREAD_MASK 4
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#define CPUCLOCK_WHICH(clock) ((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
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#define CPUCLOCK_CLOCK_MASK 3
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#define CPUCLOCK_PROF 0
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#define CPUCLOCK_VIRT 1
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#define CPUCLOCK_SCHED 2
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#define CPUCLOCK_MAX 3
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#define CLOCKFD CPUCLOCK_MAX
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#define CLOCKFD_MASK (CPUCLOCK_PERTHREAD_MASK|CPUCLOCK_CLOCK_MASK)
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#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
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((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
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#define MAKE_THREAD_CPUCLOCK(tid, clock) \
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MAKE_PROCESS_CPUCLOCK((tid), (clock) | CPUCLOCK_PERTHREAD_MASK)
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#define FD_TO_CLOCKID(fd) ((~(clockid_t) (fd) << 3) | CLOCKFD)
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#define CLOCKID_TO_FD(clk) ((unsigned int) ~((clk) >> 3))
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/* POSIX.1b interval timer structure. */
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struct k_itimer {
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struct list_head list; /* free/ allocate list */
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spinlock_t it_lock;
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clockid_t it_clock; /* which timer type */
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timer_t it_id; /* timer id */
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int it_overrun; /* overrun on pending signal */
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int it_overrun_last; /* overrun on last delivered signal */
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int it_requeue_pending; /* waiting to requeue this timer */
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#define REQUEUE_PENDING 1
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int it_sigev_notify; /* notify word of sigevent struct */
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struct signal_struct *it_signal;
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union {
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struct pid *it_pid; /* pid of process to send signal to */
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struct task_struct *it_process; /* for clock_nanosleep */
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};
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struct sigqueue *sigq; /* signal queue entry. */
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union {
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struct {
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struct hrtimer timer;
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ktime_t interval;
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} real;
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struct cpu_timer_list cpu;
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struct {
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unsigned int clock;
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unsigned int node;
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unsigned long incr;
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unsigned long expires;
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} mmtimer;
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struct alarm alarmtimer;
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struct rcu_head rcu;
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} it;
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};
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struct k_clock {
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int (*clock_getres) (const clockid_t which_clock, struct timespec *tp);
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int (*clock_set) (const clockid_t which_clock,
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const struct timespec *tp);
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int (*clock_get) (const clockid_t which_clock, struct timespec * tp);
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int (*clock_adj) (const clockid_t which_clock, struct timex *tx);
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int (*timer_create) (struct k_itimer *timer);
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int (*nsleep) (const clockid_t which_clock, int flags,
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struct timespec *, struct timespec __user *);
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long (*nsleep_restart) (struct restart_block *restart_block);
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int (*timer_set) (struct k_itimer * timr, int flags,
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struct itimerspec * new_setting,
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struct itimerspec * old_setting);
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int (*timer_del) (struct k_itimer * timr);
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#define TIMER_RETRY 1
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void (*timer_get) (struct k_itimer * timr,
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struct itimerspec * cur_setting);
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};
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extern struct k_clock clock_posix_cpu;
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extern struct k_clock clock_posix_dynamic;
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void posix_timers_register_clock(const clockid_t clock_id, struct k_clock *new_clock);
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/* function to call to trigger timer event */
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int posix_timer_event(struct k_itimer *timr, int si_private);
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void posix_cpu_timer_schedule(struct k_itimer *timer);
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void run_posix_cpu_timers(struct task_struct *task);
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void posix_cpu_timers_exit(struct task_struct *task);
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void posix_cpu_timers_exit_group(struct task_struct *task);
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void set_process_cpu_timer(struct task_struct *task, unsigned int clock_idx,
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cputime_t *newval, cputime_t *oldval);
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long clock_nanosleep_restart(struct restart_block *restart_block);
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void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new);
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#endif
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