From: Ralf Baechle <ralf@linux-mips.org>
To: Ray Will <hustos@gmail.com>
Cc: linux-mips@linux-mips.org, linux-mm@vger.kernel.org
Subject: Re: merge two insts into one in a time sensitive routing
Date: Tue, 25 Jan 2011 14:36:40 +0100 [thread overview]
Message-ID: <20110125133640.GB25526@linux-mips.org> (raw)
In-Reply-To: <AANLkTikSRmSpU+8FXOnqQ8Xm=ms=SZdrj=7WN3SLPVuJ@mail.gmail.com>
On Tue, Jan 25, 2011 at 05:04:01PM +0800, Ray Will wrote:
> The following two lines should be merged into one inst. It is the tlb
> refill handler, quite time sensitive.
> 569 uasm_i_lui(p, tmp, PM_HUGE_MASK >> 16);
> 570 uasm_i_ori(p, tmp, tmp, PM_HUGE_MASK & 0xffff);
>
> Merged to
> uasm_i_lui(p, tmp, ((PM_HUGE_MASK & 0xffff) | (PM_HUGE_MASK >> 16));
With 4K pages (=> 1M huge pages) we'd want the value 0x001fe000 to be
loaded. Your change results in in a LUI $tmp, 0xe01f instruction being
generated and that's an illegal value for the c0_pagemask register so
the operation is now architecturally undefined. Similar for other
page sizes.
All possible values for PM_HUGE_MASK will have bits set in the upper and
lower 16 halves of the register so there will always two instructions be
required to load the pagemask value.
Ralf
prev parent reply other threads:[~2011-01-25 13:37 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-25 9:04 merge two insts into one in a time sensitive routing Ray Will
2011-01-25 13:36 ` Ralf Baechle [this message]
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