From: <Tudor.Ambarus@microchip.com>
To: <alexander.sverdlin@nokia.com>, <luisalberto@google.com>
Cc: vigneshr@ti.com, bbrezillon@kernel.org, richard@nod.at,
jethro@fortanix.com, linux-kernel@vger.kernel.org,
linux-mtd@lists.infradead.org, miquel.raynal@bootlin.com,
mika.westerberg@linux.intel.com
Subject: Re: [PATCH] mtd: revert "spi-nor: intel: provide a range for poll_timout"
Date: Tue, 28 Jul 2020 08:28:22 +0000 [thread overview]
Message-ID: <afddc35d-fcef-695c-1522-df871f169a2d@microchip.com> (raw)
In-Reply-To: <ca4d6a2f-b3c8-2b52-431e-81f3cb956db7@nokia.com>
Hi, Mika,
On 7/23/20 12:05 PM, Alexander Sverdlin wrote:
>
> Hello Tudor,
>
> On 22/07/2020 19:03, Tudor.Ambarus@microchip.com wrote:
>> On 7/22/20 7:37 PM, Alexander Sverdlin wrote:
>
> [...]
>
>>> I've performed my testing as well and got the following results:
>>>
>>> Vanilla Linux 4.9 (i.e. before the introduction of the offending
>>> patch):
>>>
>>> dd if=/dev/flash/by-name/XXX of=/dev/null bs=4k
>>> 1280+0 records in
>>> 1280+0 records out
>>> 5242880 bytes (5.2 MB, 5.0 MiB) copied, 3.91981 s, 1.3 MB/s
>>>
>>> Vanilla 4.19 (i.e. with offending patch):
>>>
>>> dd if=/dev/flash/by-name/XXX of=/dev/null bs=4k
>>> 1280+0 records in
>>> 1280+0 records out
>>> 5242880 bytes (5.2 MB, 5.0 MiB) copied, 6.70891 s, 781 kB/s
>>>
>>> 4.19 + revert:
>>>
>>> dd if=/dev/flash/by-name/XXX of=/dev/null bs=4k
>>> 1280+0 records in
>>> 1280+0 records out
>>> 5242880 bytes (5.2 MB, 5.0 MiB) copied, 3.90503 s, 1.3 MB/s
>>>
[cut]
> with 10us it looks like this:
>
> dd if=/dev/flash/by-name/... of=/dev/null bs=4k
> 1280+0 records in
> 1280+0 records out
> 5242880 bytes (5.2 MB, 5.0 MiB) copied, 4.33816 s, 1.2 MB/s
>
> Which means, there is a performance regression and it would depend on
> the test case, how bad it will be...
>
We need a bit of a context here. Using a tight-loop for polling and
having a 5 secs timeout is fishy. For anything that's expected to
complete less than a few usec, it's usually better to poll continuously,
but then a timeout of 5s is way too big. Can we shrink the timeout to
few msecs?
I'll queue this to spi-nor/next to fix the perf regression, but I would
like to continue the discussion and to come up with an incremental patch
on top of this one.
Cheers,
ta
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Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2020-07-28 8:29 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 22:46 [PATCH] mtd: revert "spi-nor: intel: provide a range for poll_timout" Luis Alberto Herrera
2020-06-11 10:39 ` Mika Westerberg
2020-06-26 10:57 ` Tudor.Ambarus
2020-07-22 16:37 ` Alexander Sverdlin
2020-07-22 17:03 ` Tudor.Ambarus
2020-07-23 9:05 ` Alexander Sverdlin
2020-07-28 8:28 ` Tudor.Ambarus [this message]
2020-07-28 9:55 ` Tudor Ambarus
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