forked from luck/tmp_suning_uos_patched
cef50120b6
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> |
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| acpi | ||
| asm-generic | ||
| crypto | ||
| drm | ||
| keys | ||
| linux | ||
| math-emu | ||
| media | ||
| misc | ||
| mtd | ||
| net | ||
| pcmcia | ||
| rdma | ||
| rxrpc | ||
| scsi | ||
| sound | ||
| target | ||
| trace | ||
| video | ||
| xen | ||
| Kbuild | ||