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| author | Paul E. McKenney <paul.mckenney@linaro.org> | 2012-02-05 07:42:44 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-04-30 10:48:19 -0700 |
| commit | cef50120b61c2af4ce34bc165e19cad66296f93d (patch) | |
| tree | 963a9473155bcf6a8aa12ce92ff842242c9c3575 /kernel/rcutorture.c | |
| parent | fae4b54f28f034d228fa3bfc98858c698b64e89c (diff) | |
| download | linux-stable-cef50120b61c2af4ce34bc165e19cad66296f93d.tar.gz linux-stable-cef50120b61c2af4ce34bc165e19cad66296f93d.tar.bz2 linux-stable-cef50120b61c2af4ce34bc165e19cad66296f93d.zip | |
rcu: Direct algorithmic SRCU implementation
The current implementation of synchronize_srcu_expedited() can cause
severe OS jitter due to its use of synchronize_sched(), which in turn
invokes try_stop_cpus(), which causes each CPU to be sent an IPI.
This can result in severe performance degradation for real-time workloads
and especially for short-interation-length HPC workloads. Furthermore,
because only one instance of try_stop_cpus() can be making forward progress
at a given time, only one instance of synchronize_srcu_expedited() can
make forward progress at a time, even if they are all operating on
distinct srcu_struct structures.
This commit, inspired by an earlier implementation by Peter Zijlstra
(https://lkml.org/lkml/2012/1/31/211) and by further offline discussions,
takes a strictly algorithmic bits-in-memory approach. This has the
disadvantage of requiring one explicit memory-barrier instruction in
each of srcu_read_lock() and srcu_read_unlock(), but on the other hand
completely dispenses with OS jitter and furthermore allows SRCU to be
used freely by CPUs that RCU believes to be idle or offline.
The update-side implementation handles the single read-side memory
barrier by rechecking the per-CPU counters after summing them and
by running through the update-side state machine twice.
This implementation has passed moderate rcutorture testing on both
x86 and Power. Also updated to use this_cpu_ptr() instead of per_cpu_ptr(),
as suggested by Peter Zijlstra.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'kernel/rcutorture.c')
| -rw-r--r-- | kernel/rcutorture.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 8cd262b41499..d10b179dea83 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -639,7 +639,7 @@ static int srcu_torture_stats(char *page) cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):", torture_type, TORTURE_FLAG, idx); for_each_possible_cpu(cpu) { - cnt += sprintf(&page[cnt], " %d(%d,%d)", cpu, + cnt += sprintf(&page[cnt], " %d(%lu,%lu)", cpu, per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx], per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]); } |