Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Message-ID: <22caaecc-c954-d880-672f-45761bf7fac2@westnet.com.au>
Date:   Wed, 4 Oct 2023 22:06:29 +1000
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.15.1
Subject: Re: [PATCH 09/17] m68k: Implement xor_unlock_is_negative_byte
Content-Language: en-US
To:     Matthew Wilcox <willy@infradead.org>
Cc:     David Laight <David.Laight@aculab.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        Nicholas Piggin <npiggin@gmail.com>
References: <20230915183707.2707298-10-willy@infradead.org>
 <6e409d5f-a419-07b7-c82c-4e80fe19c6ba@westnet.com.au>
 <ZQW849TfSCK6u2f8@casper.infradead.org>
 <e1fb697714ac408e85c4e3dc573cd7d5@AcuMS.aculab.com>
 <ZQmvhC+pGWNs9R23@casper.infradead.org>
 <cffc2a427ae74f62b07345ec9348e43e@AcuMS.aculab.com>
 <ZQm67lGOBBdC2Dl9@casper.infradead.org>
 <35a33582-9206-94bb-eca2-a1d9c585f6c1@westnet.com.au>
 <ZRsi7smLotWDwoNP@casper.infradead.org>
 <9d73b9e2-502e-4ef5-bb49-bc89d478329a@westnet.com.au>
 <ZRx0lIo5i2EuIsZ/@casper.infradead.org>
From:   Greg Ungerer <gregungerer@westnet.com.au>
In-Reply-To: <ZRx0lIo5i2EuIsZ/@casper.infradead.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 4/10/23 06:07, Matthew Wilcox wrote:
> On Wed, Oct 04, 2023 at 12:14:10AM +1000, Greg Ungerer wrote:
>> On 3/10/23 06:07, Matthew Wilcox wrote:
>>> 00000918 <folio_unlock>:
>>>        918:       206f 0004       moveal %sp@(4),%a0
>>>        91c:       7001            moveq #1,%d0
>>>        91e:       b190            eorl %d0,%a0@
>>>        920:       2010            movel %a0@,%d0
>>>        922:       4a00            tstb %d0
>>>        924:       6a0a            bpls 930 <folio_unlock+0x18>
>>>        926:       42a7            clrl %sp@-
>>>        928:       2f08            movel %a0,%sp@-
>>>        92a:       4eba fafa       jsr %pc@(426 <folio_wake_bit>)
>>>        92e:       508f            addql #8,%sp
>>>        930:       4e75            rts
> 
> fwiw, here's what folio_unlock looks like today without any of my
> patches:
> 
> 00000746 <folio_unlock>:
>       746:       206f 0004       moveal %sp@(4),%a0
>       74a:       43e8 0003       lea %a0@(3),%a1
>       74e:       0891 0000       bclr #0,%a1@
>       752:       2010            movel %a0@,%d0
>       754:       4a00            tstb %d0
>       756:       6a0a            bpls 762 <folio_unlock+0x1c>
>       758:       42a7            clrl %sp@-
>       75a:       2f08            movel %a0,%sp@-
>       75c:       4eba fcc8       jsr %pc@(426 <folio_wake_bit>)
>       760:       508f            addql #8,%sp
>       762:       4e75            rts
> 
> Same number of instructions, but today's code has slightly longer insns,
> so I'm tempted to take the win?

Yes, I reckon so.


>>> We could use eori instead of eorl, at least according to table 3-9 on
>>> page 3-8:
>>>
>>> EOR Dy,<ea>x L Source ^ Destination → Destination ISA_A
>>> EORI #<data>,Dx L Immediate Data ^ Destination → Destination ISA_A
> 
> Oh.  I misread.  It only does EORI to a data register; it can't do EORI
> to an address.
> 
>> 400413e6 <folio_unlock>:
>> 400413e6:       206f 0004       moveal %sp@(4),%a0
>> 400413ea:       2010            movel %a0@,%d0
>> 400413ec:       0a80 0000 0001  eoril #1,%d0
>> 400413f2:       2080            movel %d0,%a0@
>> 400413f4:       2010            movel %a0@,%d0
>> 400413f6:       4a00            tstb %d0
>> 400413f8:       6c0a            bges 40041404 <folio_unlock+0x1e>
>> 400413fa:       42a7            clrl %sp@-
>> 400413fc:       2f08            movel %a0,%sp@-
>> 400413fe:       4eba ff30       jsr %pc@(40041330 <folio_wake_bit>)
>> 40041402:       508f            addql #8,%sp
>> 40041404:       4e75            rts
>>
>> But that is still worse anyway.
> 
> Yup.  Looks like the version I posted actually does the best!  I'll
> munge that into the patch series and repost.  Thanks for your help!

No worries. Sorry I didn't notice it earlier, but glad it is sorted now.

Regards
Greg