From: David Miller <davem@davemloft•net>
To: swise@opengridcomputing•com
Cc: rdreier@cisco•com, randy.dunlap@oracle•com,
linux-next@vger•kernel.org, linux-kernel@vger•kernel.org,
general@lists•openfabrics.org
Subject: Re: [ofa-general] [PATCH 2.6.30] RDMA/cxgb3: Remove modulo math.
Date: Tue, 10 Feb 2009 17:07:40 -0800 (PST) [thread overview]
Message-ID: <20090210.170740.208470781.davem@davemloft.net> (raw)
In-Reply-To: <499223F8.1010204@opengridcomputing.com>
From: Steve Wise <swise@opengridcomputing•com>
Date: Tue, 10 Feb 2009 19:03:52 -0600
> Roland Dreier wrote:
> > I'll roll this into the offending patch (that is in -next).
> >
> > But:
> >
> > > - wqe->recv.sgl[i].to = cpu_to_be64(((u32) wr->sg_list[i].addr) %
> > > - (1UL << (12 + page_size[i])));
> > > + wqe->recv.sgl[i].to = cpu_to_be64(((u64) wr->sg_list[i].addr) &
> > > + ((1UL << (12 + page_size[i]))-1));
> >
> > Is this required? Strength reduction optimization should do this
> > automatically (and the code has been there for quite a while, so
> > obviously it isn't causing problems)
> >
> > - R.
> >
> Ok.
GCC won't optimize that modulus the way you expect, try for yourself
and look at the assembler if you don't believe me. :-)
next prev parent reply other threads:[~2009-02-11 1:07 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-10 18:44 [ofa-general] [PATCH 2.6.30] RDMA/cxgb3: Remove modulo math Steve Wise
2009-02-10 19:04 ` [ofa-general] " Randy Dunlap
2009-02-10 19:10 ` Steve Wise
2009-02-10 19:12 ` Randy Dunlap
2009-02-11 0:38 ` [ofa-general] " Roland Dreier
2009-02-11 1:03 ` Steve Wise
[not found] ` <499223F8.1010204@opengridcomputing.com>
2009-02-11 1:07 ` David Miller [this message]
2009-02-11 1:18 ` Roland Dreier
2009-02-11 1:23 ` David Miller
2009-02-11 7:20 ` Roland Dreier
2009-02-11 8:00 ` David Miller
2009-02-11 15:44 ` Steve Wise
2009-02-11 18:12 ` Roland Dreier
2009-02-11 18:32 ` Steve Wise
2009-02-11 18:36 ` Roland Dreier
2009-02-11 18:44 ` Steve Wise
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