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List:       openvswitch-dev
Subject:    [ovs-dev] [PATCH 4/9] net: openvswitch: use this_cpu_ptr per-cpu helper
From:       cl () linux ! com (Christoph Lameter)
Date:       2012-10-31 17:39:54
Message-ID: 0000013ab7e86f8a-4adb8b81-19be-4264-96f1-924aaf3819f2-000000 () email ! amazonses ! com
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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.


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