linux-kernel - Re: [PATCH 1/2] infiniband: Help gcc generate better code for ocrdma_srq_toggle

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Date:	Sat, 31 Jan 2015 12:07:46 +0100
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	Devesh Sharma <devesh.sharma@...lex.com>,
	Selvin Xavier <selvin.xavier@...lex.com>,
	Mitesh Ahuja <mitesh.ahuja@...lex.com>
Subject: Re: [PATCH 1/2] infiniband: Help gcc generate better code for
 ocrdma_srq_toggle_bit

Hi,

Le samedi 31 janvier 2015 à 00:00 +0100, Rasmus Villemoes a écrit :
> ping
> 

As you're fixing ocrdma driver, I think you might want to find people
@emulex.com to review your patches.

BTW, there's no MAINTAINERS entry for ocrdma driver ... which is a pity.

> On Fri, Jan 16 2015, Rasmus Villemoes <linux@...musvillemoes.dk> 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 <linux@...musvillemoes.dk>
> > ---
> >  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)
> --

Regards.

-- 
Yann Droneaud
OPTEYA



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