Hi,
Tao Ren <rentao.b...@gmail.com> writes:
> On Mon, Aug 17, 2020 at 04:49:32PM +0300, Felipe Balbi wrote:
>>
>> Hi,
>>
>> rentao.b...@gmail.com writes:
>> > From: Tao Ren <rentao.b...@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.b...@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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