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Subject: Re: [PATCH v2 1/8] mmc: sdhci: Get rid of finish_tasklet
To:     Ulf Hansson <ulf.hansson@linaro.org>,
        Faiz Abbas <faiz_abbas@ti.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        DTML <devicetree@vger.kernel.org>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        linux-omap <linux-omap@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, Kishon <kishon@ti.com>,
        Chunyan Zhang <zhang.chunyan@linaro.org>,
        Grygorii Strashko <grygorii.strashko@ti.com>
References: <20190215192033.24203-1-faiz_abbas@ti.com>
 <20190215192033.24203-2-faiz_abbas@ti.com>
 <CAPDyKFqN4s1CZa9z5C3YzCUO01V-=Xhtao5352Pmytd-Tusv9A@mail.gmail.com>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Date:   Tue, 26 Mar 2019 09:33:44 +0200
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On 18/03/19 11:33 AM, Ulf Hansson wrote:
> + Arnd, Grygorii
> 
> On Fri, 15 Feb 2019 at 20:17, Faiz Abbas <faiz_abbas@ti.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@ti.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.

> 
> Kind regards
> Uffe
> 
>> ---
>>  drivers/mmc/host/sdhci.c | 43 +++++++++++++++-------------------------
>>  drivers/mmc/host/sdhci.h |  2 +-
>>  2 files changed, 17 insertions(+), 28 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index eba9bcc92ad3..20ed09b896d7 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -1232,7 +1232,7 @@ static void __sdhci_finish_mrq(struct sdhci_host *host, struct mmc_request *mrq)
>>
>>         WARN_ON(i >= SDHCI_MAX_MRQS);
>>
>> -       tasklet_schedule(&host->finish_tasklet);
>> +       host->result = IRQ_WAKE_THREAD;
>>  }
>>
>>  static void sdhci_finish_mrq(struct sdhci_host *host, struct mmc_request *mrq)
>> @@ -2705,14 +2705,6 @@ static bool sdhci_request_done(struct sdhci_host *host)
>>         return false;
>>  }
>>
>> -static void sdhci_tasklet_finish(unsigned long param)
>> -{
>> -       struct sdhci_host *host = (struct sdhci_host *)param;
>> -
>> -       while (!sdhci_request_done(host))
>> -               ;
>> -}
>> -
>>  static void sdhci_timeout_timer(struct timer_list *t)
>>  {
>>         struct sdhci_host *host;
>> @@ -2995,11 +2987,12 @@ static void sdhci_data_irq(struct sdhci_host *host, u32 intmask)
>>
>>  static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>  {
>> -       irqreturn_t result = IRQ_NONE;
>>         struct sdhci_host *host = dev_id;
>>         u32 intmask, mask, unexpected = 0;
>>         int max_loops = 16;
>>
>> +       host->result = IRQ_NONE;
>> +
>>         spin_lock(&host->lock);
>>
>>         if (host->runtime_suspended && !sdhci_sdio_irq_enabled(host)) {
>> @@ -3009,7 +3002,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>
>>         intmask = sdhci_readl(host, SDHCI_INT_STATUS);
>>         if (!intmask || intmask == 0xffffffff) {
>> -               result = IRQ_NONE;
>> +               host->result = IRQ_NONE;
>>                 goto out;
>>         }
>>
>> @@ -3054,7 +3047,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>
>>                         host->thread_isr |= intmask & (SDHCI_INT_CARD_INSERT |
>>                                                        SDHCI_INT_CARD_REMOVE);
>> -                       result = IRQ_WAKE_THREAD;
>> +                       host->result = IRQ_WAKE_THREAD;
>>                 }
>>
>>                 if (intmask & SDHCI_INT_CMD_MASK)
>> @@ -3074,7 +3067,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>                     (host->ier & SDHCI_INT_CARD_INT)) {
>>                         sdhci_enable_sdio_irq_nolock(host, false);
>>                         host->thread_isr |= SDHCI_INT_CARD_INT;
>> -                       result = IRQ_WAKE_THREAD;
>> +                       host->result = IRQ_WAKE_THREAD;
>>                 }
>>
>>                 intmask &= ~(SDHCI_INT_CARD_INSERT | SDHCI_INT_CARD_REMOVE |
>> @@ -3087,8 +3080,8 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>                         sdhci_writel(host, intmask, SDHCI_INT_STATUS);
>>                 }
>>  cont:
>> -               if (result == IRQ_NONE)
>> -                       result = IRQ_HANDLED;
>> +               if (host->result == IRQ_NONE)
>> +                       host->result = IRQ_HANDLED;
>>
>>                 intmask = sdhci_readl(host, SDHCI_INT_STATUS);
>>         } while (intmask && --max_loops);
>> @@ -3101,7 +3094,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>                 sdhci_dumpregs(host);
>>         }
>>
>> -       return result;
>> +       return host->result;
>>  }
>>
>>  static irqreturn_t sdhci_thread_irq(int irq, void *dev_id)
>> @@ -3131,6 +3124,12 @@ static irqreturn_t sdhci_thread_irq(int irq, void *dev_id)
>>                 spin_unlock_irqrestore(&host->lock, flags);
>>         }
>>
>> +       if (!isr) {
>> +               do {
>> +                       isr = !sdhci_request_done(host);
>> +               } while (isr);
>> +       }
>> +
>>         return isr ? IRQ_HANDLED : IRQ_NONE;
>>  }
>>
>> @@ -4212,12 +4211,6 @@ int __sdhci_add_host(struct sdhci_host *host)
>>         struct mmc_host *mmc = host->mmc;
>>         int ret;
>>
>> -       /*
>> -        * Init tasklets.
>> -        */
>> -       tasklet_init(&host->finish_tasklet,
>> -               sdhci_tasklet_finish, (unsigned long)host);
>> -
>>         timer_setup(&host->timer, sdhci_timeout_timer, 0);
>>         timer_setup(&host->data_timer, sdhci_timeout_data_timer, 0);
>>
>> @@ -4230,7 +4223,7 @@ int __sdhci_add_host(struct sdhci_host *host)
>>         if (ret) {
>>                 pr_err("%s: Failed to request IRQ %d: %d\n",
>>                        mmc_hostname(mmc), host->irq, ret);
>> -               goto untasklet;
>> +               return ret;
>>         }
>>
>>         ret = sdhci_led_register(host);
>> @@ -4263,8 +4256,6 @@ int __sdhci_add_host(struct sdhci_host *host)
>>         sdhci_writel(host, 0, SDHCI_INT_ENABLE);
>>         sdhci_writel(host, 0, SDHCI_SIGNAL_ENABLE);
>>         free_irq(host->irq, host);
>> -untasklet:
>> -       tasklet_kill(&host->finish_tasklet);
>>
>>         return ret;
>>  }
>> @@ -4326,8 +4317,6 @@ void sdhci_remove_host(struct sdhci_host *host, int dead)
>>         del_timer_sync(&host->timer);
>>         del_timer_sync(&host->data_timer);
>>
>> -       tasklet_kill(&host->finish_tasklet);
>> -
>>         if (!IS_ERR(mmc->supply.vqmmc))
>>                 regulator_disable(mmc->supply.vqmmc);
>>
>> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
>> index 6cc9a3c2ac66..624d5aa01995 100644
>> --- a/drivers/mmc/host/sdhci.h
>> +++ b/drivers/mmc/host/sdhci.h
>> @@ -554,7 +554,7 @@ struct sdhci_host {
>>
>>         unsigned int desc_sz;   /* ADMA descriptor size */
>>
>> -       struct tasklet_struct finish_tasklet;   /* Tasklet structures */
>> +       irqreturn_t result;     /* Result of IRQ handler */
>>
>>         struct timer_list timer;        /* Timer for timeouts */
>>         struct timer_list data_timer;   /* Timer for data timeouts */
>> --
>> 2.19.2
>>
>