Re: [PATCHv2 net-next 04/12] sctp: implement make_datafrag for sctp_stream_interleave
flat view
From: Xin Long <lucien.xin@gmail.com>
Date: 2017-12-08 17:37:15
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netdev
On Sat, Dec 9, 2017 at 1:29 AM, David Laight [off-list ref] wrote:
From: Xin Long ...quoted
Hi, David, Sorry, I'm not sure we're worrying about the cpu cost or codes style now ? For cpu cost, I think 0x848(%r13) operation must be better than the generated code of if-else.Nope - the call xxx(%ryyy) is likely to be a data cache miss and a complete cpu pipeline stall. The conditional will be a data cache hit and the code (for one branch) will be prefetched and speculatively executed. Some very modern cpu might manage to predict indirect jumps, but for most it is a full pipeline stall.
Thanks for the CPU information. The thing is with if-else can't avoid xxx(%ryyy) in this case, as Marcelo said above. It seems if-else will just be a extra cost compare to this one.