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Message-ID: <ef84d2dd-84ea-e1c7-05ef-f0a082d4f7d0@opensource.wdc.com>
Date:   Tue, 9 Aug 2022 07:57:51 -0700
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Subject: Re: [ata] 0568e61225: stress-ng.copy-file.ops_per_sec -15.0%
 regression
Content-Language: en-US
To:     John Garry <john.garry@huawei.com>,
        kernel test robot <oliver.sang@intel.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        linux-ide@vger.kernel.org, lkp@lists.01.org, lkp@intel.com,
        ying.huang@intel.com, feng.tang@intel.com,
        zhengjun.xing@linux.intel.com, fengwei.yin@intel.com
References: <YuzPMMnnY739Tnit@xsang-OptiPlex-9020>
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 <16f03f81-a8c7-bacf-c74c-67231f7f7202@huawei.com>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <16f03f81-a8c7-bacf-c74c-67231f7f7202@huawei.com>
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On 2022/08/09 7:16, John Garry wrote:
> On 09/08/2022 10:58, John Garry wrote:
>>>>
>>>> commit: 0568e6122574dcc1aded2979cd0245038efe22b6 ("ata: libata-scsi:=
=20
>>>> cap ata_device->max_sectors according to shost->max_sectors")
>>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git mas=
ter
>>>>
>>>> in testcase: stress-ng
>>>> on test machine: 96 threads 2 sockets Ice Lake with 256G memory
>>>> with following parameters:
>>>>
>>>> =C2=A0=C2=A0=C2=A0=C2=A0nr_threads: 10%
>>>> =C2=A0=C2=A0=C2=A0=C2=A0disk: 1HDD
>>>> =C2=A0=C2=A0=C2=A0=C2=A0testtime: 60s
>>>> =C2=A0=C2=A0=C2=A0=C2=A0fs: f2fs
>>>> =C2=A0=C2=A0=C2=A0=C2=A0class: filesystem
>>>> =C2=A0=C2=A0=C2=A0=C2=A0test: copy-file
>>>> =C2=A0=C2=A0=C2=A0=C2=A0cpufreq_governor: performance
>>>> =C2=A0=C2=A0=C2=A0=C2=A0ucode: 0xb000280
>>>
>>> Without knowing what the device adapter is, hard to say where the=20
>>> problem is. I
>>> suspect that with the patch applied, we may be ending up with a small=
=20
>>> default
>>> max_sectors value, causing overhead due to more commands than necessa=
ry.
>>>
>>> Will check what I see with my test rig.
>>
>> As far as I can see, this patch should not make a difference unless th=
e=20
>> ATA shost driver is setting the max_sectors value unnecessarily low.
>=20
> For __ATA_BASE_SHT, we don't set max_sectors. As such, we default=20
> shost->max_sectors =3D SCSI_DEFAULT_MAX_SECTORS (=3D1024) in=20
> scsi_host_alloc(). I assume no shost dma mapping limit applied.
>=20
> Then - for example - we could select dev->max_sectors =3D=20
> ATA_MAX_SECTORS_LBA48 (=3D65535) in ata_dev_configure().
>=20
> So with commit 0568e6122574 we would have final max sectors =3D 1024, a=
s=20
> opposed to 65535 previously. I guess that the problem is something like=
=20
> this.
>=20
> If so, it seems that we would need to apply the shost dma mapping limit=
=20
> separately in ata_scsi_dev_config() and not use shost->max_sectors.

OK. Will have a look at that.

>=20
> thanks,
> John
>=20


--=20
Damien Le Moal
Western Digital Research