From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760783AbbA3XAK (ORCPT ); Fri, 30 Jan 2015 18:00:10 -0500 Received: from mail-lb0-f178.google.com ([209.85.217.178]:36099 "EHLO mail-lb0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753771AbbA3XAG (ORCPT ); Fri, 30 Jan 2015 18:00:06 -0500 From: Rasmus Villemoes To: Roland Dreier Cc: Sean Hefty , Hal Rosenstock , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] infiniband: Help gcc generate better code for ocrdma_srq_toggle_bit Organization: D03 References: <1421419196-4659-1-git-send-email-linux@rasmusvillemoes.dk> X-Hashcash: 1:20:150130:linux-rdma@vger.kernel.org::gNtaFJgIHEdnVaQo:000000000000000000000000000000000000a8m X-Hashcash: 1:20:150130:hal.rosenstock@gmail.com::6jcBo/X/3hiT2Rvh:00000000000000000000000000000000000000PZ1 X-Hashcash: 1:20:150130:sean.hefty@intel.com::Ak8ACSnJ2pM8NCIY:000000000000000000000000000000000000000001YDE X-Hashcash: 1:20:150130:roland@kernel.org::DLCXMh+WTzkR66au:000000000000000000000000000000000000000000003I37 X-Hashcash: 1:20:150130:linux-kernel@vger.kernel.org::fuP6/WxX6ZcdgyIR:0000000000000000000000000000000005oFy Date: Sat, 31 Jan 2015 00:00:02 +0100 In-Reply-To: <1421419196-4659-1-git-send-email-linux@rasmusvillemoes.dk> (Rasmus Villemoes's message of "Fri, 16 Jan 2015 15:39:55 +0100") Message-ID: <87twz7ho25.fsf@rasmusvillemoes.dk> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ping On Fri, Jan 16 2015, Rasmus Villemoes wrote: > gcc emits a surprising amount of code in order to flip a bit. One > would think that a single instruction is enough. > > $ scripts/bloat-o-meter /tmp/ocrdma_verbs.o drivers/infiniband/hw/ocrdma/ocrdma_verbs.o > add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-142 (-142) > function old new delta > ocrdma_post_srq_recv 498 460 -38 > ocrdma_poll_cq 2010 1962 -48 > ocrdma_discard_cqes 495 439 -56 > > All three calls of ocrdma_srq_toggle_bit happen within spinlocks, so > saving a few useless instructions might be worthwhile. > > Signed-off-by: Rasmus Villemoes > --- > drivers/infiniband/hw/ocrdma/ocrdma_verbs.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c b/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c > index fb8d8c4dfbb9..eff11e6c6183 100644 > --- a/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c > +++ b/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c > @@ -1484,10 +1484,7 @@ static void ocrdma_srq_toggle_bit(struct ocrdma_srq *srq, int idx) > int i = idx / 32; > unsigned int mask = (1 << (idx % 32)); > > - if (srq->idx_bit_fields[i] & mask) > - srq->idx_bit_fields[i] &= ~mask; > - else > - srq->idx_bit_fields[i] |= mask; > + srq->idx_bit_fields[i] ^= mask; > } > > static int ocrdma_hwq_free_cnt(struct ocrdma_qp_hwq_info *q)