• Ulf Hansson's avatar
    mmc: core: Optimize boot time by detecting cards simultaneously · 520bd7a8
    Ulf Hansson authored
    The mmc workqueue is an ordered workqueue, allowing only one work to
    execute per given time. As this workqueue is used for card detection, the
    conseqeunce is that cards will be detected one by one waiting for each
    other.
    
    Moreover, most of the time spent during card initialization is waiting for
    the card's internal firmware to be ready. From a CPU perspective this
    typically means waiting for a completion variable to be kicked via an
    IRQ-handler or waiting for a sleep timer to finish.
    
    This behaviour of detecting/initializing cards is sub-optimal, especially
    for SOCs having several controllers/cards.
    
    Let's convert to use the system_freezable_wq for the mmc detect works.
    This enables several works to be executed simultaneously and thus also
    cards to be detected like so.
    
    Tests on UX500, which holds two eMMC cards and an SD-card (actually also
    an SDIO card, currently not detected), shows a significant improved
    behaviour due to this change.
    
    Before this change, both the eMMC cards waited for the SD card to be
    initialized as its detect work entered the workqueue first. In some cases,
    depending on the characteristic of the SD-card, they got delayed 1-1.5 s.
    
    Additionally for the second eMMC, it needed to wait for the first eMMC to
    be initialized which added another 120-190 ms.
    
    Converting to the system_freezable_wq, removed these delays and made both
    the eMMC cards available far earlier in the boot sequence.
    
    Selecting the system_freezable_wq, in favour of for example the system_wq,
    is because we need card detection mechanism to be disabled once userspace
    are frozen during system PM. Currently the mmc core deal with this via PM
    notifiers, but following patches may utilize the behaviour of the
    system_freezable_wq, to simplify the use of the PM notifiers.
    Signed-off-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
    Tested-by: default avatarAlan Cooper <alcooperx@gmail.com>
    Tested-by: default avatarShawn Lin <shawn.lin@rock-chips.com>
    520bd7a8
core.c 70.6 KB