| Message ID | 50910A04.5000003@gmail.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
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. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 1 Nov 2012, Shan Wei wrote: > 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); What does current guarantee that? If it is guaranteed then you can use the __this_cpu_xxx ops. > 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() Right. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Nov 1, 2012 at 7:33 AM, Christoph Lameter <cl@linux.com> wrote: > On Thu, 1 Nov 2012, Shan Wei wrote: > >> 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); > > What does current guarantee that? If it is guaranteed then you can use the > __this_cpu_xxx ops. Preemption is disabled in all of the places where writes are done and all of the reads are from foreign CPUs. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 1 Nov 2012, Jesse Gross wrote: > On Thu, Nov 1, 2012 at 7:33 AM, Christoph Lameter <cl@linux.com> wrote: > > On Thu, 1 Nov 2012, Shan Wei wrote: > > > >> 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); > > > > What does current guarantee that? If it is guaranteed then you can use the > > __this_cpu_xxx ops. > > Preemption is disabled in all of the places where writes are done and > all of the reads are from foreign CPUs. Since preemption is disabled no processor change can occur. So its safe to use __this_cpu ops throughout and they will operate on the current per cpu area. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c index 4c4b62c..77d16a5 100644 --- 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); /* Extract flow from 'skb' into 'key'. */ error = ovs_flow_extract(skb, p->port_no, &key, &key_len); @@ -282,7 +282,7 @@ int ovs_dp_upcall(struct datapath *dp, struct sk_buff *skb, return 0; err: - stats = per_cpu_ptr(dp->stats_percpu, smp_processor_id()); + stats = this_cpu_ptr(dp->stats_percpu); u64_stats_update_begin(&stats->sync); stats->n_lost++; diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c index 03779e8..70af0be 100644 --- a/net/openvswitch/vport.c +++ b/net/openvswitch/vport.c @@ -333,8 +333,7 @@ void ovs_vport_receive(struct vport *vport, struct sk_buff *skb) { struct vport_percpu_stats *stats; - stats = per_cpu_ptr(vport->percpu_stats, smp_processor_id()); - + stats = this_cpu_ptr(vport->percpu_stats); u64_stats_update_begin(&stats->sync); stats->rx_packets++; stats->rx_bytes += skb->len; @@ -359,7 +358,7 @@ int ovs_vport_send(struct vport *vport, struct sk_buff *skb) if (likely(sent)) { struct vport_percpu_stats *stats; - stats = per_cpu_ptr(vport->percpu_stats, smp_processor_id()); + stats = this_cpu_ptr(vport->percpu_stats); u64_stats_update_begin(&stats->sync); stats->tx_packets++;