fc2219d49e
These issues identified during an old-fashioned face-to-face code review extended over many hours. o Bury various forms of the "rsp->completed == rsp->gpnum" comparison into an rcu_gp_in_progress() function, which has the beneficial side-effect of forcing consistent use of ACCESS_ONCE(). o Replace hand-coded arithmetic with DIV_ROUND_UP(). o Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])" instances into an rcu_preempted_readers() function, as this expression indicates that there are no readers blocked within RCU read-side critical sections blocking the current grace period. (Though there might well be similar readers blocking the next grace period.) o Remove a dangling rcu_restart_cpu() declaration that has been dangling for almost 20 minor releases of the kernel. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246442687-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
260 lines
9.8 KiB
C
260 lines
9.8 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright IBM Corporation, 2008
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/cache.h>
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#include <linux/spinlock.h>
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#include <linux/threads.h>
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#include <linux/cpumask.h>
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#include <linux/seqlock.h>
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/*
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* Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT.
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* In theory, it should be possible to add more levels straightforwardly.
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* In practice, this has not been tested, so there is probably some
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* bug somewhere.
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*/
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#define MAX_RCU_LVLS 3
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#define RCU_FANOUT (CONFIG_RCU_FANOUT)
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#define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
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#define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)
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#if NR_CPUS <= RCU_FANOUT
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# define NUM_RCU_LVLS 1
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# define NUM_RCU_LVL_0 1
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# define NUM_RCU_LVL_1 (NR_CPUS)
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# define NUM_RCU_LVL_2 0
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# define NUM_RCU_LVL_3 0
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#elif NR_CPUS <= RCU_FANOUT_SQ
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# define NUM_RCU_LVLS 2
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# define NUM_RCU_LVL_0 1
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# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
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# define NUM_RCU_LVL_2 (NR_CPUS)
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# define NUM_RCU_LVL_3 0
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#elif NR_CPUS <= RCU_FANOUT_CUBE
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# define NUM_RCU_LVLS 3
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# define NUM_RCU_LVL_0 1
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# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ)
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# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
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# define NUM_RCU_LVL_3 NR_CPUS
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#else
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# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
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#endif /* #if (NR_CPUS) <= RCU_FANOUT */
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#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
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#define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
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/*
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* Dynticks per-CPU state.
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*/
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struct rcu_dynticks {
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int dynticks_nesting; /* Track nesting level, sort of. */
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int dynticks; /* Even value for dynticks-idle, else odd. */
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int dynticks_nmi; /* Even value for either dynticks-idle or */
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/* not in nmi handler, else odd. So this */
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/* remains even for nmi from irq handler. */
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};
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/*
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* Definition for node within the RCU grace-period-detection hierarchy.
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*/
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struct rcu_node {
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spinlock_t lock;
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long gpnum; /* Current grace period for this node. */
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/* This will either be equal to or one */
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/* behind the root rcu_node's gpnum. */
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unsigned long qsmask; /* CPUs or groups that need to switch in */
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/* order for current grace period to proceed.*/
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unsigned long qsmaskinit;
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/* Per-GP initialization for qsmask. */
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unsigned long grpmask; /* Mask to apply to parent qsmask. */
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int grplo; /* lowest-numbered CPU or group here. */
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int grphi; /* highest-numbered CPU or group here. */
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u8 grpnum; /* CPU/group number for next level up. */
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u8 level; /* root is at level 0. */
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struct rcu_node *parent;
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struct list_head blocked_tasks[2];
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/* Tasks blocked in RCU read-side critsect. */
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} ____cacheline_internodealigned_in_smp;
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/* Index values for nxttail array in struct rcu_data. */
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#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
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#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
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#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
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#define RCU_NEXT_TAIL 3
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#define RCU_NEXT_SIZE 4
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/* Per-CPU data for read-copy update. */
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struct rcu_data {
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/* 1) quiescent-state and grace-period handling : */
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long completed; /* Track rsp->completed gp number */
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/* in order to detect GP end. */
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long gpnum; /* Highest gp number that this CPU */
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/* is aware of having started. */
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long passed_quiesc_completed;
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/* Value of completed at time of qs. */
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bool passed_quiesc; /* User-mode/idle loop etc. */
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bool qs_pending; /* Core waits for quiesc state. */
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bool beenonline; /* CPU online at least once. */
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bool preemptable; /* Preemptable RCU? */
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struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
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unsigned long grpmask; /* Mask to apply to leaf qsmask. */
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/* 2) batch handling */
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/*
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* If nxtlist is not NULL, it is partitioned as follows.
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* Any of the partitions might be empty, in which case the
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* pointer to that partition will be equal to the pointer for
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* the following partition. When the list is empty, all of
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* the nxttail elements point to nxtlist, which is NULL.
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*
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* [*nxttail[RCU_NEXT_READY_TAIL], NULL = *nxttail[RCU_NEXT_TAIL]):
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* Entries that might have arrived after current GP ended
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* [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
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* Entries known to have arrived before current GP ended
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* [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
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* Entries that batch # <= ->completed - 1: waiting for current GP
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* [nxtlist, *nxttail[RCU_DONE_TAIL]):
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* Entries that batch # <= ->completed
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* The grace period for these entries has completed, and
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* the other grace-period-completed entries may be moved
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* here temporarily in rcu_process_callbacks().
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*/
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struct rcu_head *nxtlist;
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struct rcu_head **nxttail[RCU_NEXT_SIZE];
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long qlen; /* # of queued callbacks */
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long blimit; /* Upper limit on a processed batch */
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#ifdef CONFIG_NO_HZ
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/* 3) dynticks interface. */
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struct rcu_dynticks *dynticks; /* Shared per-CPU dynticks state. */
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int dynticks_snap; /* Per-GP tracking for dynticks. */
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int dynticks_nmi_snap; /* Per-GP tracking for dynticks_nmi. */
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#endif /* #ifdef CONFIG_NO_HZ */
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/* 4) reasons this CPU needed to be kicked by force_quiescent_state */
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#ifdef CONFIG_NO_HZ
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unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */
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#endif /* #ifdef CONFIG_NO_HZ */
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unsigned long offline_fqs; /* Kicked due to being offline. */
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unsigned long resched_ipi; /* Sent a resched IPI. */
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/* 5) __rcu_pending() statistics. */
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long n_rcu_pending; /* rcu_pending() calls since boot. */
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long n_rp_qs_pending;
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long n_rp_cb_ready;
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long n_rp_cpu_needs_gp;
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long n_rp_gp_completed;
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long n_rp_gp_started;
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long n_rp_need_fqs;
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long n_rp_need_nothing;
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int cpu;
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};
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/* Values for signaled field in struct rcu_state. */
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#define RCU_GP_INIT 0 /* Grace period being initialized. */
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#define RCU_SAVE_DYNTICK 1 /* Need to scan dyntick state. */
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#define RCU_FORCE_QS 2 /* Need to force quiescent state. */
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#ifdef CONFIG_NO_HZ
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#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
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#else /* #ifdef CONFIG_NO_HZ */
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#define RCU_SIGNAL_INIT RCU_FORCE_QS
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#endif /* #else #ifdef CONFIG_NO_HZ */
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#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
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#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
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#define RCU_SECONDS_TILL_STALL_CHECK (10 * HZ) /* for rsp->jiffies_stall */
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#define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ) /* for rsp->jiffies_stall */
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#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
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/* to take at least one */
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/* scheduling clock irq */
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/* before ratting on them. */
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#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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/*
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* RCU global state, including node hierarchy. This hierarchy is
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* represented in "heap" form in a dense array. The root (first level)
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* of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
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* level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
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* and the third level in ->node[m+1] and following (->node[m+1] referenced
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* by ->level[2]). The number of levels is determined by the number of
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* CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy"
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* consisting of a single rcu_node.
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*/
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struct rcu_state {
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struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
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struct rcu_node *level[NUM_RCU_LVLS]; /* Hierarchy levels. */
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u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */
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u8 levelspread[NUM_RCU_LVLS]; /* kids/node in each level. */
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struct rcu_data *rda[NR_CPUS]; /* array of rdp pointers. */
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/* The following fields are guarded by the root rcu_node's lock. */
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u8 signaled ____cacheline_internodealigned_in_smp;
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/* Force QS state. */
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long gpnum; /* Current gp number. */
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long completed; /* # of last completed gp. */
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spinlock_t onofflock; /* exclude on/offline and */
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/* starting new GP. */
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spinlock_t fqslock; /* Only one task forcing */
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/* quiescent states. */
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unsigned long jiffies_force_qs; /* Time at which to invoke */
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/* force_quiescent_state(). */
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unsigned long n_force_qs; /* Number of calls to */
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/* force_quiescent_state(). */
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unsigned long n_force_qs_lh; /* ~Number of calls leaving */
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/* due to lock unavailable. */
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unsigned long n_force_qs_ngp; /* Number of calls leaving */
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/* due to no GP active. */
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#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
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unsigned long gp_start; /* Time at which GP started, */
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/* but in jiffies. */
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unsigned long jiffies_stall; /* Time at which to check */
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/* for CPU stalls. */
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#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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#ifdef CONFIG_NO_HZ
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long dynticks_completed; /* Value of completed @ snap. */
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#endif /* #ifdef CONFIG_NO_HZ */
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};
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#ifdef RCU_TREE_NONCORE
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/*
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* RCU implementation internal declarations:
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*/
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extern struct rcu_state rcu_sched_state;
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DECLARE_PER_CPU(struct rcu_data, rcu_sched_data);
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extern struct rcu_state rcu_bh_state;
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DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
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#ifdef CONFIG_TREE_PREEMPT_RCU
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extern struct rcu_state rcu_preempt_state;
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DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data);
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#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
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#endif /* #ifdef RCU_TREE_NONCORE */
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