• Sujit Reddy Thumma's avatar
    mmc: core: Use delayed work in clock gating framework · 597dd9d7
    Sujit Reddy Thumma authored
    Current clock gating framework disables the MCI clock as soon as the
    request is completed and enables it when a request arrives. This aggressive
    clock gating framework, when enabled, cause following issues:
    
    When there are back-to-back requests from the Queue layer, we unnecessarily
    end up disabling and enabling the clocks between these requests since 8MCLK
    clock cycles is a very short duration compared to the time delay between
    back to back requests reaching the MMC layer. This overhead can effect the
    overall performance depending on how long the clock enable and disable
    calls take which is platform dependent. For example on some platforms we
    can have clock control not on the local processor, but on a different
    subsystem and the time taken to perform the clock enable/disable can add
    significant overhead.
    
    Also if the host controller driver decides to disable the host clock too
    when mmc_set_ios function is called with ios.clock=0, it adds additional
    delay and it is highly possible that the next request had already arrived
    and unnecessarily blocked in enabling the clocks. This is seen frequently
    when the processor is executing at high speeds and in multi-core platforms
    thus reduces the overall throughput compared to if clock gating is
    disabled.
    
    Fix this by delaying turning off the clocks by posting request on
    delayed workqueue. Also cancel the unscheduled pending work, if any,
    when there is access to card.
    
    sysfs entry is provided to tune the delay as needed, default
    value set to 200ms.
    Signed-off-by: default avatarSujit Reddy Thumma <sthumma@codeaurora.org>
    Acked-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    Signed-off-by: default avatarChris Ball <cjb@laptop.org>
    597dd9d7
mmc-dev-attrs.txt 2.8 KB