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Date: Wed, 21 Jan 2009 06:13:41 -0800 From: ebiederm@...ssion.com (Eric W. Biederman) To: Stephen Hemminger <shemminger@...tta.com> Cc: Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>, Rusty Russell <rusty@...tcorp.com.au>, Herbert Xu <herbert@...dor.apana.org.au>, akpm@...ux-foundation.org, hpa@...or.com, brgerst@...il.com, cl@...ux-foundation.org, travis@....com, linux-kernel@...r.kernel.org, steiner@....com, hugh@...itas.com, "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> Subject: Re: [PATCH] percpu: add optimized generic percpu accessors Stephen Hemminger <shemminger@...tta.com> writes: > This is crap. only a small fraction of these SNMP counters are > close enough to the hot path to deserve per-cpu treatment. Interesting. I was just reading af_inet.c:ipv4_mib_init_net() to get a feel for what a large consumer of percpu counters looks like. I expect the patterns I saw will hold even if the base size is much smaller. Your statement reinforces my point that our allocations in a per cpu area are small and our dynamic per cpu allocator is not really optimized for small allocations. In most places what we want are 1-5 counters, which is max 40 bytes. And our minimum allocation is a full cache line (64-128 bytes) per allocation. I'm wondering if dynamic per cpu allocations should work more like slab. Have a set of percpu base pointers for an area, and return an area + offset in some convenient form. Ideally we would just have one area (allowing us to keep the base pointer in a register), but I'm not convinced that doesn't fall down in the face of dynamic allocation. Eric -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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