netdev - Re: [PATCH net-next 0/6] bpf: introduce per-cpu maps

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Date:	Sat, 06 Feb 2016 03:35:10 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ast@...com
Cc:	kafai@...com, tom.leiming@...il.com, daniel@...earbox.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/6] bpf: introduce per-cpu maps

From: Alexei Starovoitov <ast@...com>
Date: Mon, 1 Feb 2016 22:39:52 -0800

> We've started to use bpf to trace every packet and atomic add
> instruction (event JITed) started to show up in perf profile.
> The solution is to do per-cpu counters.
> For PERCPU_(HASH|ARRAY) map the existing bpf_map_lookup() helper
> returns per-cpu area which bpf programs can use to store and
> increment the counters. The BPF_MAP_LOOKUP_ELEM syscall command
> returns areas from all cpus and user process aggregates the counters.
> The usage example is in patch 6. The api turned out to be very
> easy to use from bpf program and from user space.
> Long term we were discussing to add 'bounded loop' instruction,
> so bpf programs can do aggregation within the program which may
> help some use cases. Right now user space aggregation of
> per-cpu counters fits the best.
> 
> This patch set is new approach for per-cpu hash and array maps.
> I've reused the map tests written by Martin and Ming, but
> implementation and api is new. Old discussion here:
> http://thread.gmane.org/gmane.linux.kernel/2123800/focus=2126435

Series applied, thanks Alexei.