linux-kernel - Re: [PATCH v2 1/8] mmc: sdhci: Get rid of finish

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Date:   Tue, 2 Apr 2019 13:29:10 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, Kishon <kishon@...com>,
        Chunyan Zhang <zhang.chunyan@...aro.org>,
        Grygorii Strashko <grygorii.strashko@...com>
Subject: Re: [PATCH v2 1/8] mmc: sdhci: Get rid of finish_tasklet

Hi Adrian,

On 26/03/19 1:03 PM, Adrian Hunter wrote:
> On 18/03/19 11:33 AM, Ulf Hansson wrote:
>> + Arnd, Grygorii
>>
>> On Fri, 15 Feb 2019 at 20:17, Faiz Abbas <faiz_abbas@...com> wrote:
>>>
>>> sdhci.c has two bottom halves implemented. A threaded_irq for handling
>>> card insert/remove operations and a tasklet for finishing mmc requests.
>>> With the addition of external dma support, dmaengine APIs need to
>>> terminate in non-atomic context before unmapping the dma buffers.
>>>
>>> To facilitate this, remove the finish_tasklet and move the call of
>>> sdhci_request_done() to the threaded_irq() callback. Also move the
>>> interrupt result variable to sdhci_host so it can be populated from
>>> anywhere inside the sdhci_irq handler.
>>>
>>> Signed-off-by: Faiz Abbas <faiz_abbas@...com>
>>
>> Adrian, I think it makes sense to apply this patch, even if there is
>> very minor negative impact throughput wise.
>>
>> To me, it doesn't seems like MMC/SD/SDIO has good justification for
>> using tasklets, besides from the legacy point of view, of course.
>> Instead, I think we should try to move all mmc hosts into using
>> threaded IRQs.
>>
>> So, what do you think? Can you overlook the throughput drop and
>> instead we can try to recover this on top with other optimizations?
> 
> I tend to favour good results as expressed here:
> 
> 	https://lkml.org/lkml/2007/6/22/360
> 
> So I want to do optimization first.
> 
> But performance is not the only problem with the patch.  Give me a few
> days and I will see what I can come up with.
> 

Gentle ping on this.

Thanks,
Faiz