From: Jon Hunter <jonathanh@nvidia.com>
To: Mark Brown <broonie@kernel.org>, Martin Sperl <kernel@martin.sperl.org>
Cc: linux-tegra <linux-tegra@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
<linux-spi@vger.kernel.org>
Subject: Re: Regression: spi: core: avoid waking pump thread from spi_sync instead run teardown delayed
Date: Wed, 16 Jan 2019 11:01:37 +0000 [thread overview]
Message-ID: <b6d6585b-86ce-5eae-842e-83561beefa61@nvidia.com> (raw)
In-Reply-To: <20190115212539.GK5522@sirena.org.uk>
On 15/01/2019 21:25, Mark Brown wrote:
> On Tue, Jan 15, 2019 at 09:58:55PM +0100, Martin Sperl wrote:
>
>> Maybe a bigger change to the reduce the complexity of
>> the state machine would solve that problem and also
>> reduce code complexity...
>
> Yeah, that's where I was getting to with that test patch I posted.
>
>> I may find some time over the weekend if no solution
>> has been found until then.
>
> Thanks for volunteering :)
>
>> The way I would envision it it would have a “state”
>> as a level (0=shutdown, 1=hw enabled, 2=in pump,
>> 3=in transfer, 4=in hw-mode,...) and a complete
>> to allow waking the shutdown thread (and by this
>> avoiding the busy wait loop we have now).
>> This would replace those idling, busy, and running flags.
>
> That's a good idea, yes - a single enum much more reflects what we can
> actually do in terms of transitions.
>
>> Drawback: it is invasive, but let us see what it
>> really looks like...
>
> I think we need to either drop your change (which would be bad since it
> is a big performance improvement, I'd punted it for later when I did the
> original refactoring to push the work into the caller threads then never
> got around to it) or have a invasive changes to make the new situation
> clearer. Right now things are just far too complex to reason about
> which isn't helping anyone.
What I am seeing on Tegra is that the SPI controller is no longer
runtime-pm suspended and so while this may improve performance, I think
that this change is going to have a negative impact on idle power.
I would be surprised if this problem is specific to Tegra because I
don't see how the controller's busy state can ever be cleared :-(
Cheers
Jon
--
nvpublic
next prev parent reply other threads:[~2019-01-16 11:01 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-14 15:35 Regression: spi: core: avoid waking pump thread from spi_sync instead run teardown delayed Jon Hunter
[not found] ` <7C4A5EFC-8235-40C8-96E1-E6020529DF72@martin.sperl.org>
2019-01-15 14:26 ` Jon Hunter
2019-01-15 15:10 ` Mark Brown
2019-01-15 16:09 ` Jon Hunter
2019-01-15 19:27 ` Mark Brown
2019-01-15 17:39 ` kernel
2019-01-15 19:26 ` Mark Brown
2019-01-15 20:58 ` Martin Sperl
2019-01-15 21:25 ` Mark Brown
2019-01-16 11:01 ` Jon Hunter [this message]
2019-01-18 17:11 ` kernel
2019-01-18 19:12 ` Mark Brown
2019-01-20 11:24 ` kernel
2019-01-23 17:56 ` Mark Brown
2019-05-09 19:47 ` Martin Sperl
2019-05-12 8:54 ` Mark Brown
2019-01-16 10:58 ` Jon Hunter
2019-01-22 9:36 ` Geert Uytterhoeven
[not found] ` <CGME20190123082650eucas1p243ce21346a00e9b3e9eed2863cd3d280@eucas1p2.samsung.com>
2019-01-23 8:26 ` Marek Szyprowski
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