From mboxrd@z Thu Jan  1 00:00:00 1970
From: Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH RFC 22/39] mmc: block: Prepare CQE data
Date: Fri, 10 Mar 2017 10:29:36 +0200
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Cc: Ulf Hansson <ulf.hansson@linaro.org>, linux-mmc <linux-mmc@vger.kernel.org>, Alex Lemberg <alex.lemberg@sandisk.com>, Mateusz Nowak <mateusz.nowak@intel.com>, Yuliy Izrailov <Yuliy.Izrailov@sandisk.com>, Jaehoon Chung <jh80.chung@samsung.com>, Dong Aisheng <dongas86@gmail.com>, Das Asutosh <asutoshd@codeaurora.org>, Zhangfei Gao <zhangfei.gao@gmail.com>, Dorfman Konstantin <kdorfman@codeaurora.org>, David Griego <david.griego@linaro.org>, Sahitya Tummala <stummala@codeaurora.org>, Harjani Ritesh <riteshh@codeaurora.org>, Venu Byravarasu <vbyravarasu@nvidia.com>
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On 10/03/17 00:39, Linus Walleij wrote:
> On Fri, Mar 3, 2017 at 1:22 PM, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 15/02/17 15:49, Linus Walleij wrote:
>>> On Fri, Feb 10, 2017 at 1:55 PM, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>
>>>> Enhance mmc_blk_data_prep() to support CQE requests.
>>>>
>>>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>>>
>>> Hey:
>>>
>>>> +#include <linux/ioprio.h>
>>> (...)
>>>> +       if (IOPRIO_PRIO_CLASS(req_get_ioprio(req)) == IOPRIO_CLASS_RT)
>>>> +               brq->data.flags |= MMC_DATA_PRIO;
>>>
>>> What is this?
>>
>> It is the command queue priority.
>>
>> The command queue supports 2 priorities: "high" (1) and "simple" (0).  The
>> eMMC will give "high" priority tasks priority over "simple" priority tasks.
>>
>> So here we give priority to IOPRIO_CLASS_RT which seems appropriate.
> 
> So if I understand correctly, you are obtaining the block layer scheduling
> priorities, that can (only?) be set by ionice has from the command line?

AFAICS it is the ioprio_set() system call .

> 
> We need to discuss this with the block maintainers.
> 
> I'm not so sure about the future of this. The IOPRIO is only used with the CFQ
> scheduler, only two other sites in the kernel use this and MQ and its schedulers
> surely does not have ionice handling as far as I know.
> 
> The BFQ does not use it, AFAIK it is using different heuristics to prioritize
> block traffic, and that does not include using ionice hints.
> 
> Is ionice:ing something we're really going to do going forward?
> Should this be repurposed so that the block scheduler use this prio to
> communicate to the driver layer to prioritize certain traffic?

That seems like a separate issue.  At the moment, I/O priorities are what we
have, and giving priority to RT seems appropriate.