From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 3 Oct 2013 15:35:19 +1000 From: Michael Ellerman To: Sukadev Bhattiprolu Subject: Re: [PATCH 5/9][v5] powerpc: implement is_instr_load_store(). Message-ID: <20131003053519.GC17237@concordia> References: <1380672911-12812-1-git-send-email-sukadev@linux.vnet.ibm.com> <1380672911-12812-6-git-send-email-sukadev@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1380672911-12812-6-git-send-email-sukadev@linux.vnet.ibm.com> Cc: Michael Ellerman , linux-kernel@vger.kernel.org, Stephane Eranian , linuxppc-dev@ozlabs.org, Paul Mackerras , Arnaldo Carvalho de Melo , Anshuman Khandual List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Oct 01, 2013 at 05:15:06PM -0700, Sukadev Bhattiprolu wrote: > Implement is_instr_load_store() to detect whether a given instruction > is one of the fixed-point or floating-point load/store instructions. > This function will be used in a follow-on patch to save memory hierarchy > information of the load/store. The search over the array is a bit of a pity, especially as the worst case penalises you when you haven't hit a load/store. I think we can do better. If you look at the opcode maps, and in particular the extended table for opcode 31, you'll see there's a reasonable amount of structure. The following is only valid for arch 2.06, ie. it will classify reserved opcodes as being load/store, but I think that's fine for the moment. If we need to use it somewhere in future we can update it. But we should add a big comment saying it's only valid in that case. Anyway, I think the following logic is all we need for opcode 31: bool is_load_store(int ext_opcode) { upper = ext_opcode >> 5; lower = ext_opcode & 0x1f; /* Short circuit as many misses as we can */ if (lower < 3 || lower > 23) return false; if (lower == 3) if (upper >= 16) return true; return false; if (lower == 6) if (upper <= 1) return true; return false; if (lower == 7 || lower == 12) return true; if (lower >= 20) /* && lower <= 23 (implicit) */ return true; return false; } Which is not pretty, but I think it's preferable to the full search over the array. cheers