diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2022-03-08 15:45:33 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-05-03 10:20:57 -0700 |
| commit | 282d8998e9979c2186af7f7d22366f2fc3149838 (patch) | |
| tree | a89b3241fcd01074c023062015e24de1440f5066 /include/linux/srcutree.h | |
| parent | c2445d38785086422e56dcbe049b73a53b2ba81f (diff) | |
| download | lwn-282d8998e9979c2186af7f7d22366f2fc3149838.tar.gz lwn-282d8998e9979c2186af7f7d22366f2fc3149838.zip | |
srcu: Prevent expedited GPs and blocking readers from consuming CPU
If an SRCU reader blocks while a synchronize_srcu_expedited() waits for
that same reader, then that grace period will spawn an endless series of
workqueue handlers, consuming a full CPU. This quickly gets pointless
because consuming more CPU isn't going to make that reader get done
faster, especially if it is blocked waiting for an external event.
This commit therefore spawns at most one pair of back-to-back workqueue
handlers per expedited grace period phase, instead inserting increasing
delays as that grace period phase grows older, but capped at 10 jiffies.
In any case, if there have been at least 100 back-to-back workqueue
handlers within a single jiffy, regardless of grace period or grace-period
phase, then a one-jiffy delay is inserted.
[ paulmck: Apply feedback from kernel test robot. ]
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Reported-by: Song Liu <song@kernel.org>
Tested-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'include/linux/srcutree.h')
| -rw-r--r-- | include/linux/srcutree.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 1b9ff4ed37e4..e3014319d1ad 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -71,9 +71,11 @@ struct srcu_struct { unsigned long srcu_gp_seq; /* Grace-period seq #. */ unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ + unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */ unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */ unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */ unsigned long srcu_n_lock_retries; /* Contention events in current interval. */ + unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */ struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ bool sda_is_static; /* May ->sda be passed to free_percpu()? */ unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */ @@ -83,6 +85,8 @@ struct srcu_struct { atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */ /* callback for the barrier */ /* operation. */ + unsigned long reschedule_jiffies; + unsigned long reschedule_count; struct delayed_work work; struct lockdep_map dep_map; }; |