Re: [PATCH v3] mmc: core: Add support for idle time BKOPS

[Ulf Hansson]

On 3 December 2012 10:49,  <merez@xxxxxxxxxxxxxx> wrote:
> Hi Jaehoon,
>
> With this patch we don't expect to see any degradation. Thanks for
> verifying that.
> The test plan would be to run the lmdd and iozone benchmarks with this
> patch and verify that the performance is not degraded.
> I verified it with the msm_sdcc controller.
>
> Chris - We do expect it to influence the battery consumption, since we now
> delay getting into suspend (since mmc_start_bkops which is called after
> the delayed work is executed claims the host).
> The solution for that should be done by the controller which can shorten
> the timeout given to pm_schedule_suspend by the periodic BKOPS idle time.
> Does it make sense to you?
>
> Thanks,
> Maya
> On Thu, November 29, 2012 4:40 am, Jaehoon Chung wrote:
>> Hi Maya,
>>
>> Thank you a lot for working idle time BKOPS.
>>
>> I tested with this patch. It's working fine.(Suspend/resume is also
>> working well.)
>> Test controller is sdhci controller.
>> When i tested the performance with iozone, i didn't find that performance
>> is decreased.
>> Well, as Chris is mentioned, do you have any test plan?
>> So I will test more with this patch, because i want to test with dw-mmc
>> controller, too.
>>
>> On 11/25/2012 08:56 PM, Maya Erez wrote:
>>> Devices have various maintenance operations need to perform internally.
>>> In order to reduce latencies during time critical operations like read
>>> and write, it is better to execute maintenance operations in other
>>> times - when the host is not being serviced. Such operations are called
>>> Background operations (BKOPS).
>>> The device notifies the status of the BKOPS need by updating
>>> BKOPS_STATUS
>>> (EXT_CSD byte [246]).
>>>
>>> According to the standard a host that supports BKOPS shall check the
>>> status periodically and start background operations as needed, so that
>>> the device has enough time for its maintenance operations.
>>>
>>> This patch adds support for this periodic check of the BKOPS status.
>>> Since foreground operations are of higher priority than background
>>> operations the host will check the need for BKOPS when it is idle,
>>> and in case of an incoming request the BKOPS operation will be
>>> interrupted.
>>>
>>> When the mmcqd thread is idle, a delayed work is created to check the
>>> need for BKOPS. The time to start the delayed work is calculated based
>>> on the host controller suspend timeout, in case it was set. If not, a
>>> default time is used.

What host controller suspend timeout are you referring to here?

If you are thinking of the runtime PM autosuspend timeout used in many
host driver, then you might have missunderstand how runtime PM is used
in host drivers.
This has nothing to do with BKOPS as such, unless you think that the
card must be kept clocked during BKOPS operations, but then this needs
to be stated somewhere in this patch and that is not the case.

Moreover, I could not find any new timeout added for the _host_ struct
in this patch.

>>> If BKOPS are required in level 1, which is non-blocking, there will be
>>> polling of the card status to wait for the BKOPS completion and prevent
>>> suspend that will interrupt the BKOPS.

Not sure of what suspend you are talking about here. But for sure
BKOPS must _never_ prevent a system suspend.

You might want to prevent a host from being runtime suspended though,
but that is not accomplished in this patch.

>>> If the card raised an exception, the need for urgent BKOPS (level 2/3)
>>> will be checked immediately and if needed, the BKOPS will be performed
>>> without waiting for the next idle time.
>>>
>>> Signed-off-by: Maya Erez <merez@xxxxxxxxxxxxxx>
>>>
>>> ---
>>> This patch is based on the periodic BKOPS implementation in version 8 of
>>> "support BKOPS feature for eMMC" patch.
>>> The patch was modified to answer the following issues:
>>> - In order to prevent a race condition between going into suspend and
>>> starting BKOPS,
>>>   the suspend timeout of the host controller is taking into accound in
>>> determination of the start time
>>>   of the delayed work
>>> - Since mmc_start_bkops is called from two contexts now, mmc_claim_host
>>> was moved to the beginning of the function
>>> - Also, the check of doing_bkops should be protected when determing if
>>> an HPI is needed due to the same reason.
>>>
>>> Changes in v3:
>>>     - Move the call to stop_bkops to block.c.
>>>       This allows us to remove the mmc_claim_host from inside the
>>> function and doesn't cause additional degradation
>>>       due to un-neccessary calim host operation
>>>
>>> Changes in v2:
>>>     - Check the number of written / discarded sectors as the trigger for
>>> checking the BKOPS need.
>>>     - Code review fixes
>>>
>>> ---
>>>  drivers/mmc/card/block.c |    8 ++-
>>>  drivers/mmc/card/queue.c |    2 +
>>>  drivers/mmc/core/core.c  |  178
>>> +++++++++++++++++++++++++++++++++++++++++++---
>>>  drivers/mmc/core/mmc.c   |   23 ++++++
>>>  include/linux/mmc/card.h |   35 +++++++++
>>>  include/linux/mmc/core.h |    3 +
>>>  6 files changed, 237 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>>> index 172a768..40b4ae3 100644
>>> --- a/drivers/mmc/card/block.c
>>> +++ b/drivers/mmc/card/block.c
>>> @@ -1394,9 +1394,15 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq,
>>> struct request *req)
>>>      struct mmc_blk_data *md = mq->data;
>>>      struct mmc_card *card = md->queue.card;
>>>
>>> -    if (req && !mq->mqrq_prev->req)
>>> +    if (req && !mq->mqrq_prev->req) {
>>>              /* claim host only for the first request */
>>>              mmc_claim_host(card->host);
>>> +            if (card->ext_csd.bkops_en &&
>>> +                card->bkops_info.started_delayed_bkops) {
>>> +                            card->bkops_info.started_delayed_bkops = false;
>>> +                            mmc_stop_bkops(card);
>> We didn't need to check whether mmc_stop_bkops is success or not?
>> If mmc_stop_bkops() is failed, then bkops is continuously running.
>>
>> Best Regards,
>> Jaehoon Chung
>>
>>> +            }
>>> +    }
>>>
>>>      ret = mmc_blk_part_switch(card, md);
>>>      if (ret) {
>>> diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
>>> index fadf52e..9d0c96a 100644
>>> --- a/drivers/mmc/card/queue.c
>>> +++ b/drivers/mmc/card/queue.c
>>> @@ -51,6 +51,7 @@ static int mmc_queue_thread(void *d)
>>>  {
>>>      struct mmc_queue *mq = d;
>>>      struct request_queue *q = mq->queue;
>>> +    struct mmc_card *card = mq->card;
>>>
>>>      current->flags |= PF_MEMALLOC;
>>>
>>> @@ -83,6 +84,7 @@ static int mmc_queue_thread(void *d)
>>>                              set_current_state(TASK_RUNNING);
>>>                              break;
>>>                      }
>>> +                    mmc_start_delayed_bkops(card);
>>>                      up(&mq->thread_sem);
>>>                      schedule();
>>>                      down(&mq->thread_sem);
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index 06c42cf..72ae15b 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -253,9 +253,36 @@ mmc_start_request(struct mmc_host *host, struct
>>> mmc_request *mrq)
>>>  }
>>>
>>>  /**
>>> + * mmc_start_delayed_bkops() - Start a delayed work to check for
>>> + *      the need of non urgent BKOPS
>>> + *
>>> + * @card: MMC card to start BKOPS on
>>> + */
>>> +void mmc_start_delayed_bkops(struct mmc_card *card)
>>> +{
>>> +    if (!card || !card->ext_csd.bkops_en || mmc_card_doing_bkops(card))
>>> +            return;
>>> +
>>> +    pr_debug("%s: %s: queueing delayed_bkops_work\n",
>>> +             mmc_hostname(card->host), __func__);
>>> +
>>> +    /*
>>> +     * cancel_delayed_bkops_work will prevent a race condition between
>>> +     * fetching a request by the mmcqd and the delayed work, in case
>>> +     * it was removed from the queue work but not started yet
>>> +     */
>>> +    card->bkops_info.cancel_delayed_work = false;
>>> +    card->bkops_info.started_delayed_bkops = true;
>>> +    queue_delayed_work(system_nrt_wq, &card->bkops_info.dw,
>>> +                       msecs_to_jiffies(
>>> +                               card->bkops_info.delay_ms));
>>> +}
>>> +EXPORT_SYMBOL(mmc_start_delayed_bkops);
>>> +
>>> +/**
>>>   *  mmc_start_bkops - start BKOPS for supported cards
>>>   *  @card: MMC card to start BKOPS
>>> - *  @form_exception: A flag to indicate if this function was
>>> + *  @from_exception: A flag to indicate if this function was
>>>   *                   called due to an exception raised by the card
>>>   *
>>>   *  Start background operations whenever requested.
>>> @@ -269,25 +296,47 @@ void mmc_start_bkops(struct mmc_card *card, bool
>>> from_exception)
>>>      bool use_busy_signal;
>>>
>>>      BUG_ON(!card);
>>> -
>>> -    if (!card->ext_csd.bkops_en || mmc_card_doing_bkops(card))
>>> +    if (!card->ext_csd.bkops_en)
>>>              return;
>>>
>>> +    mmc_claim_host(card->host);
>>> +
>>> +    if ((card->bkops_info.cancel_delayed_work) && !from_exception) {
>>> +            pr_debug("%s: %s: cancel_delayed_work was set, exit\n",
>>> +                     mmc_hostname(card->host), __func__);
>>> +            card->bkops_info.cancel_delayed_work = false;
>>> +            goto out;
>>> +    }
>>> +
>>> +    if (mmc_card_doing_bkops(card)) {
>>> +            pr_debug("%s: %s: already doing bkops, exit\n",
>>> +                     mmc_hostname(card->host), __func__);
>>> +            goto out;
>>> +    }
>>> +
>>>      err = mmc_read_bkops_status(card);
>>>      if (err) {
>>>              pr_err("%s: Failed to read bkops status: %d\n",
>>>                     mmc_hostname(card->host), err);
>>> -            return;
>>> +            goto out;
>>>      }
>>>
>>>      if (!card->ext_csd.raw_bkops_status)
>>> -            return;
>>> +            goto out;
>>>
>>> +    pr_info("%s: %s: card->ext_csd.raw_bkops_status = 0x%x\n",
>>> +            mmc_hostname(card->host), __func__,
>>> +            card->ext_csd.raw_bkops_status);
>>> +
>>> +    /*
>>> +     * If the function was called due to exception but there is no need
>>> +     * for urgent BKOPS, BKOPs will be performed by the delayed BKOPs
>>> +     * work, before going to suspend
>>> +     */
>>>      if (card->ext_csd.raw_bkops_status < EXT_CSD_BKOPS_LEVEL_2 &&
>>>          from_exception)
>>> -            return;
>>> +            goto out;
>>>
>>> -    mmc_claim_host(card->host);
>>>      if (card->ext_csd.raw_bkops_status >= EXT_CSD_BKOPS_LEVEL_2) {
>>>              timeout = MMC_BKOPS_MAX_TIMEOUT;
>>>              use_busy_signal = true;
>>> @@ -309,13 +358,108 @@ void mmc_start_bkops(struct mmc_card *card, bool
>>> from_exception)
>>>       * bkops executed synchronously, otherwise
>>>       * the operation is in progress
>>>       */
>>> -    if (!use_busy_signal)
>>> +    if (!use_busy_signal) {
>>>              mmc_card_set_doing_bkops(card);
>>> +            pr_debug("%s: %s: starting the polling thread\n",
>>> +                     mmc_hostname(card->host), __func__);
>>> +            queue_work(system_nrt_wq,
>>> +                       &card->bkops_info.poll_for_completion);
>>> +    }
>>> +
>>>  out:
>>>      mmc_release_host(card->host);
>>>  }
>>>  EXPORT_SYMBOL(mmc_start_bkops);
>>>
>>> +/**
>>> + * mmc_bkops_completion_polling() - Poll on the card status to
>>> + * wait for the non-blocking BKOPS completion
>>> + * @work:   The completion polling work
>>> + *
>>> + * The on-going reading of the card status will prevent the card
>>> + * from getting into suspend while it is in the middle of
>>> + * performing BKOPS.

Not true! Suspend will not be prevented by doing a mmc_send_status.
Moreover, I would be interested to understand more about why you need
to prevent "suspend". Please elaborate why you think this is needed.

>>> + * Since the non blocking BKOPS can be interrupted by a fetched
>>> + * request we also check IF mmc_card_doing_bkops in each
>>> + * iteration.
>>> + */
>>> +void mmc_bkops_completion_polling(struct work_struct *work)
>>> +{
>>> +    struct mmc_card *card = container_of(work, struct mmc_card,
>>> +                    bkops_info.poll_for_completion);
>>> +    unsigned long timeout_jiffies = jiffies +
>>> +            msecs_to_jiffies(BKOPS_COMPLETION_POLLING_TIMEOUT_MS);
>>> +    u32 status;
>>> +    int err;
>>> +
>>> +    /*
>>> +     * Wait for the BKOPs to complete. Keep reading the status to prevent
>>> +     * the host from getting into suspend
>>> +     */
>>> +    do {
>>> +            mmc_claim_host(card->host);
>>> +
>>> +            if (!mmc_card_doing_bkops(card))
>>> +                    goto out;
>>> +
>>> +            err = mmc_send_status(card, &status);
>>> +            if (err) {
>>> +                    pr_err("%s: error %d requesting status\n",
>>> +                           mmc_hostname(card->host), err);
>>> +                    goto out;
>>> +            }
>>> +
>>> +            /*
>>> +             * Some cards mishandle the status bits, so make sure to check
>>> +             * both the busy indication and the card state.
>>> +             */
>>> +            if ((status & R1_READY_FOR_DATA) &&
>>> +                (R1_CURRENT_STATE(status) != R1_STATE_PRG)) {
>>> +                    pr_debug("%s: %s: completed BKOPs, exit polling\n",
>>> +                             mmc_hostname(card->host), __func__);
>>> +                    mmc_card_clr_doing_bkops(card);
>>> +                    card->bkops_info.started_delayed_bkops = false;
>>> +                    goto out;
>>> +            }
>>> +
>>> +            mmc_release_host(card->host);
>>> +
>>> +            /*
>>> +             * Sleep before checking the card status again to allow the
>>> +             * card to complete the BKOPs operation
>>> +             */
>>> +            msleep(BKOPS_COMPLETION_POLLING_INTERVAL_MS);
>>> +    } while (time_before(jiffies, timeout_jiffies));
>>> +
>>> +    pr_err("%s: %s: exit polling due to timeout\n",
>>> +           mmc_hostname(card->host), __func__);
>>> +
>>> +    return;
>>> +out:
>>> +    mmc_release_host(card->host);
>>> +}
>>> +
>>> +/**
>>> + * mmc_start_idle_time_bkops() - check if a non urgent BKOPS is
>>> + * needed
>>> + * @work:   The idle time BKOPS work
>>> + */
>>> +void mmc_start_idle_time_bkops(struct work_struct *work)
>>> +{
>>> +    struct mmc_card *card = container_of(work, struct mmc_card,
>>> +                    bkops_info.dw.work);
>>> +
>>> +    /*
>>> +     * Prevent a race condition between mmc_stop_bkops and the delayed
>>> +     * BKOPS work in case the delayed work is executed on another CPU
>>> +     */
>>> +    if (card->bkops_info.cancel_delayed_work)
>>> +            return;
>>> +
>>> +    mmc_start_bkops(card, false);
>>> +}
>>> +EXPORT_SYMBOL(mmc_start_idle_time_bkops);
>>> +
>>>  static void mmc_wait_done(struct mmc_request *mrq)
>>>  {
>>>      complete(&mrq->completion);
>>> @@ -582,6 +726,17 @@ int mmc_stop_bkops(struct mmc_card *card)
>>>      int err = 0;
>>>
>>>      BUG_ON(!card);
>>> +
>>> +    /*
>>> +     * Notify the delayed work to be cancelled, in case it was already
>>> +     * removed from the queue, but was not started yet
>>> +     */
>>> +    card->bkops_info.cancel_delayed_work = true;
>>> +    if (delayed_work_pending(&card->bkops_info.dw))
>>> +            cancel_delayed_work_sync(&card->bkops_info.dw);
>>> +    if (!mmc_card_doing_bkops(card))
>>> +            goto out;
>>> +
>>>      err = mmc_interrupt_hpi(card);
>>>
>>>      /*
>>> @@ -593,6 +748,7 @@ int mmc_stop_bkops(struct mmc_card *card)
>>>              err = 0;
>>>      }
>>>
>>> +out:
>>>      return err;
>>>  }
>>>  EXPORT_SYMBOL(mmc_stop_bkops);
>>> @@ -2506,15 +2662,15 @@ int mmc_pm_notify(struct notifier_block
>>> *notify_block,
>>>      switch (mode) {
>>>      case PM_HIBERNATION_PREPARE:
>>>      case PM_SUSPEND_PREPARE:
>>> -            if (host->card && mmc_card_mmc(host->card) &&
>>> -                mmc_card_doing_bkops(host->card)) {
>>> +            if (host->card && mmc_card_mmc(host->card)) {
>>> +                    mmc_claim_host(host);
>>>                      err = mmc_stop_bkops(host->card);
>>> +                    mmc_release_host(host);

This code seems a bit strange. You will check for mmc_card_mmc, but
not all (e)MMC will support bkops. How about acually just checking if
bkops is "on" or "off" somehow.

Additionally, so this piece of code shall stop an ongoing bkops before
going to suspend, so that make sense. But would it not be more
meaningfull to take care of that in mmc_suspend_host? I mean why do yo
need to do it in the PM_SUSPEND_PREPARE notification sequence
especially?

>>>                      if (err) {
>>>                              pr_err("%s: didn't stop bkops\n",
>>>                                      mmc_hostname(host));
>>>                              return err;
>>>                      }
>>> -                    mmc_card_clr_doing_bkops(host->card);
>>>              }
>>>
>>>              spin_lock_irqsave(&host->lock, flags);
>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>> index 7cc4638..dba76e3 100644
>>> --- a/drivers/mmc/core/mmc.c
>>> +++ b/drivers/mmc/core/mmc.c
>>> @@ -1258,6 +1258,29 @@ static int mmc_init_card(struct mmc_host *host,
>>> u32 ocr,
>>>              }
>>>      }
>>>
>>> +    if (!oldcard) {
>>> +            if (card->ext_csd.bkops_en) {
>>> +                    INIT_DELAYED_WORK(&card->bkops_info.dw,
>>> +                                      mmc_start_idle_time_bkops);
>>> +                    INIT_WORK(&card->bkops_info.poll_for_completion,
>>> +                              mmc_bkops_completion_polling);

I guess you don't have "removable" eMMC with BKOPS support so this
code will in practice only be executed once for an eMMC, so we are
safe. But still I am not fond of putting this code for workqueue here.
Either that should be done as a part of when the card is
created/deleted or when then host is created/deleted.

>>> +
>>> +                    /*
>>> +                     * Calculate the time to start the BKOPs checking.
>>> +                     * The idle time of the host controller should be taken
>>> +                     * into account in order to prevent a race condition
>>> +                     * before starting BKOPs and going into suspend.
>>> +                     * If the host controller didn't set its idle time,
>>> +                     * a default value is used.
>>> +                     */
>>> +                    card->bkops_info.delay_ms = MMC_IDLE_BKOPS_TIME_MS;
>>> +                    if (card->bkops_info.host_suspend_tout_ms)
>>> +                            card->bkops_info.delay_ms = min(
>>> +                                    card->bkops_info.delay_ms,
>>> +                                  card->bkops_info.host_suspend_tout_ms/2);
>>> +            }
>>> +    }
>>> +
>>>      if (!oldcard)
>>>              host->card = card;
>>>
>>> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
>>> index 943550d..224e2a5 100644
>>> --- a/include/linux/mmc/card.h
>>> +++ b/include/linux/mmc/card.h
>>> @@ -208,6 +208,39 @@ struct mmc_part {
>>>  #define MMC_BLK_DATA_AREA_GP        (1<<2)
>>>  };
>>>
>>> +/**
>>> + * struct mmc_bkops_info - BKOPS data
>>> + * @dw:     Idle time bkops delayed work
>>> + * @host_suspend_tout_ms:   The host controller idle time,
>>> + * before getting into suspend
>>> + * @delay_ms:       The time to start the BKOPS
>>> + *        delayed work once MMC thread is idle
>>> + * @poll_for_completion:    Poll on BKOPS completion
>>> + * @cancel_delayed_work: A flag to indicate if the delayed work
>>> + *        should be cancelled
>>> + * @started_delayed_bkops:  A flag to indicate if the delayed
>>> + *        work was scheduled
>>> + * @sectors_changed:  number of  sectors written or
>>> + *       discard since the last idle BKOPS were scheduled
>>> + */
>>> +struct mmc_bkops_info {
>>> +    struct delayed_work     dw;
>>> +    unsigned int            host_suspend_tout_ms;

As stated earlier, what is this timeout you are referring to? What suspend?

>>> +    unsigned int            delay_ms;
>>> +/*
>>> + * A default time for checking the need for non urgent BKOPS once mmcqd
>>> + * is idle.
>>> + */
>>> +#define MMC_IDLE_BKOPS_TIME_MS 2000
>>> +    struct work_struct      poll_for_completion;
>>> +/* Polling timeout and interval for waiting on non-blocking BKOPs
>>> completion */
>>> +#define BKOPS_COMPLETION_POLLING_TIMEOUT_MS 10000 /* in ms */
>>> +#define BKOPS_COMPLETION_POLLING_INTERVAL_MS 1000 /* in ms */
>>> +    bool                    cancel_delayed_work;
>>> +    bool                    started_delayed_bkops;
>>> +    unsigned int            sectors_changed;

Could not find "sectors_changed" being used. Maybe you forgot to
remove this from previous version of the patch.

>>> +};
>>> +
>>>  /*
>>>   * MMC device
>>>   */
>>> @@ -276,6 +309,8 @@ struct mmc_card {
>>>      struct dentry           *debugfs_root;
>>>      struct mmc_part part[MMC_NUM_PHY_PARTITION]; /* physical partitions */
>>>      unsigned int    nr_parts;
>>> +
>>> +    struct mmc_bkops_info   bkops_info;
>>>  };
>>>
>>>  /*
>>> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
>>> index 9b9cdaf..665d345 100644
>>> --- a/include/linux/mmc/core.h
>>> +++ b/include/linux/mmc/core.h
>>> @@ -145,6 +145,9 @@ extern int mmc_app_cmd(struct mmc_host *, struct
>>> mmc_card *);
>>>  extern int mmc_wait_for_app_cmd(struct mmc_host *, struct mmc_card *,
>>>      struct mmc_command *, int);
>>>  extern void mmc_start_bkops(struct mmc_card *card, bool
>>> from_exception);
>>> +extern void mmc_start_delayed_bkops(struct mmc_card *card);
>>> +extern void mmc_start_idle_time_bkops(struct work_struct *work);
>>> +extern void mmc_bkops_completion_polling(struct work_struct *work);
>>>  extern int __mmc_switch(struct mmc_card *, u8, u8, u8, unsigned int,
>>> bool);
>>>  extern int mmc_switch(struct mmc_card *, u8, u8, u8, unsigned int);
>>>
>>>
>>
>>
>
>
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Finally some overall thoughts. What I would like to understand is how
we decide that the card has become "idle". I belive two values should
be considered, but are they?
1. The card need BKOPS to be performed for some status level.
2. Request inactivity for a certain timeout has occured.

Have you considered to use runtime PM for the card device instead of
the workqueue?

Kind regards
Ulf Hansson
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