Christoph Lameter said, at 2012/11/1 1:39: > On Wed, 31 Oct 2012, Shan Wei wrote: > >> --- a/net/openvswitch/datapath.c >> +++ b/net/openvswitch/datapath.c >> @@ -208,7 +208,7 @@ void ovs_dp_process_received_packet(struct vport *p, >> struct sk_buff *skb) >> int error; >> int key_len; >> >> - stats = per_cpu_ptr(dp->stats_percpu, smp_processor_id()); >> + stats = this_cpu_ptr(dp->stats_percpu); > > Well this is an improvement and may be ok if the preemption is disabled at > this point. There is another possibility here to use this_cpu_read/add/inc > instead of determining the pointer to the local cpu first and then > performing operations on the fields. The pointer relocation with > this_cpu_xxx ops is implicit in the instructions and safe against changing > of processors. It would also save us the determination of a pointer to the > current cpus stats structure.
yes, this_cpu_ptr just locate the point to current cpu per-cpu data domain. and then operating [read/write/inc/sub] fields of this per-cpu variable maybe on other cpu because task is rescheduled for preemption, interrupt. But for different field in same per-cpu variable, how to guarantee n_missed and n_hit are from same cpu? this_cpu_read(dp->stats_percpu->n_missed); [processor changed] this_cpu_read(dp->stats_percpu->n_hit); In addition, following usage of per_cpu_ptr can be replaced by this_cpu_read. cpu=get_cpu() .... *per_cpu_ptr(p,cpu) .... .... put_cpu() -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
