From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rasmus Villemoes Subject: Re: [PATCH 1/2] infiniband: Help gcc generate better code for ocrdma_srq_toggle_bit Date: Sat, 31 Jan 2015 00:00:02 +0100 Message-ID: <87twz7ho25.fsf@rasmusvillemoes.dk> References: <1421419196-4659-1-git-send-email-linux@rasmusvillemoes.dk> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <1421419196-4659-1-git-send-email-linux-qQsb+v5E8BnlAoU/VqSP6n9LOBIZ5rWg@public.gmane.org> (Rasmus Villemoes's message of "Fri, 16 Jan 2015 15:39:55 +0100") Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Roland Dreier Cc: Sean Hefty , Hal Rosenstock , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@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) -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html