linux-kernel - Re: [PATCH] dmatest: add ability to disable pq and xor

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Date:	Tue, 4 Jun 2013 17:11:51 +0000
From:	Dan Williams <djbw@...com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Jon Mason <jon.mason@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Jiang <dave.jiang@...el.com>,
	Vinod Koul <vinod.koul@...el.com>
Subject: Re: [PATCH] dmatest: add ability to disable pq and xor


On 6/4/13 12:25 AM, "Andy Shevchenko" <andy.shevchenko@...il.com> wrote:

>On Tue, Jun 4, 2013 at 2:29 AM, Jon Mason <jon.mason@...el.com> wrote:
>> On Fri, May 31, 2013 at 11:22:10AM +0300, Andy Shevchenko wrote:
>>> On Fri, May 17, 2013 at 8:54 PM, Jon Mason <jon.mason@...el.com> wrote:
>>> > dmatest would create a thread to stress XOR and PQ, if the
>>>capability is
>>> > present in the hardware.  Add the ability to disable XOR and PQ by
>>> > disabling it if *_sources are set to zero.
>>>
>>> Sorry, didn't comment this earlier.
>>>
>>> Those threads are independent including MEMCPY stuff.
>>> I think it's better to have one additional parameter let's say
>>> type_of_test where you can set
>>> 1 for MEMCPY
>>> 2 for XOR
>>> 4 for PQ
>>>
>>> Share this parameter via debugfs and use 0x07 as default value.
>>> I doubt we need this as a module parameter.
>>
>> This is using the existing module parameter, so there is nothing new
>> added.
>
>That's why it's a bit confusing. User can more easily forget the
>'magic' numbers. And I see no reason to prevent user to enter 0 as a
>number of sources.

Well, source counts less than 2 are invalid for these operations, but that
is besides the point.

>Moreover, your patch doesn't cover the case when user doesn't want to
>run MEMCPY thread.

Yes, this is what I wanted to point out.  If we're adding per operation
type selection, might as well enable memcpy to be controlled too.
Especially if we just use a bitmap_and() with the dma_cap_mask() to pick
which tests to run.  Might also encourage some slave-op test types to be
added as well.

>
>>  Since the testing is started immediately upon module
>> insertion,
>
>It used to be so, but nowadays it's true only when dmatest is compiled in.
>If someone wants to compile in that module they probably want to run
>stress tests, where XOR and PQ might be useful.

...and they would want the test selection to be specified on the kernel
command line.  At least that's how I used compiled in dmatest in the past.

>
>> there needs to be a way to prevent it from ever starting.
>
>My opinion I already shared, new node under debugfs. There is might be
>a good reason to add a new module parameter as well.

I'm not seeing why debugfs is helpful here.  Just make it a module
parameter that calls a routine to setup the bit mask.

--
Dan

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