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    SubjectRe: [PATCH] usb: gadget: aspeed: fixup vhub port irq handling
    Date

    Hi,

    Tao Ren <rentao.bupt@gmail.com> writes:
    > On Mon, Aug 17, 2020 at 04:49:32PM +0300, Felipe Balbi wrote:
    >>
    >> Hi,
    >>
    >> rentao.bupt@gmail.com writes:
    >> > From: Tao Ren <rentao.bupt@gmail.com>
    >> >
    >> > This is a follow-on patch for commit a23be4ed8f48 ("usb: gadget: aspeed:
    >> > improve vhub port irq handling"): for_each_set_bit() is replaced with
    >> > simple for() loop because for() loop runs faster on ASPEED BMC.
    >> >
    >> > Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
    >> > ---
    >> > drivers/usb/gadget/udc/aspeed-vhub/core.c | 10 +++-------
    >> > drivers/usb/gadget/udc/aspeed-vhub/vhub.h | 3 +++
    >> > 2 files changed, 6 insertions(+), 7 deletions(-)
    >> >
    >> > diff --git a/drivers/usb/gadget/udc/aspeed-vhub/core.c b/drivers/usb/gadget/udc/aspeed-vhub/core.c
    >> > index cdf96911e4b1..be7bb64e3594 100644
    >> > --- a/drivers/usb/gadget/udc/aspeed-vhub/core.c
    >> > +++ b/drivers/usb/gadget/udc/aspeed-vhub/core.c
    >> > @@ -135,13 +135,9 @@ static irqreturn_t ast_vhub_irq(int irq, void *data)
    >> >
    >> > /* Handle device interrupts */
    >> > if (istat & vhub->port_irq_mask) {
    >> > - unsigned long bitmap = istat;
    >> > - int offset = VHUB_IRQ_DEV1_BIT;
    >> > - int size = VHUB_IRQ_DEV1_BIT + vhub->max_ports;
    >> > -
    >> > - for_each_set_bit_from(offset, &bitmap, size) {
    >> > - i = offset - VHUB_IRQ_DEV1_BIT;
    >> > - ast_vhub_dev_irq(&vhub->ports[i].dev);
    >> > + for (i = 0; i < vhub->max_ports; i++) {
    >> > + if (istat & VHUB_DEV_IRQ(i))
    >> > + ast_vhub_dev_irq(&vhub->ports[i].dev);
    >>
    >> how have you measured your statement above? for_each_set_bit() does
    >> exactly what you did. Unless your architecture has an instruction which
    >> helps finds the next set bit (like cls on ARM), which, then, makes it
    >> much faster.
    >
    > I did some testing and result shows for() loop runs faster than
    > for_each_set_bit() loop. Please refer to details below (discussion with
    > Benjamin in the original patch) and kindly let me know your suggestions.

    no strong feelings, just surprised that you're already worried about
    20~40 cycles of cpu time ;-)

    Patch applied for next merge window

    --
    balbi
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