Re: [PATCH v2 1/8] mmc: sdhci: Get rid of finish_tasklet

Adrian Hunter
2019-03-26T07:33:44Z

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
>>
>