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

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Date:	Mon, 2 Feb 2015 12:58:44 +0000
From:	Selvin Xavier <Selvin.Xavier@...lex.Com>
To:	Yann Droneaud <ydroneaud@...eya.com>,
	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-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Devesh Sharma <Devesh.Sharma@...lex.Com>,
	Mitesh Ahuja <Mitesh.Ahuja@...lex.Com>
Subject: RE: [PATCH 1/2] infiniband: Help gcc generate better code for
 ocrdma_srq_toggle_bit

Thank you Yann Droneaud for forwarding this mail.

We will add  an entry for ocrdma driver in MAINTAINERS file.

Thanks,
Selvin Xavier

> -----Original Message-----
> From: Yann Droneaud [mailto:ydroneaud@...eya.com]
> Sent: Saturday, January 31, 2015 4:38 PM
> To: Rasmus Villemoes
> Cc: Roland Dreier; Sean Hefty; Hal Rosenstock; linux-rdma@...r.kernel.org;
> linux-kernel@...r.kernel.org; Devesh Sharma; Selvin Xavier; Mitesh Ahuja
> 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
> 
>