On Mon, Aug 31, 2020 at 12:54:57PM +0300, Felipe Balbi wrote: > > 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
Thanks Felipe. Ben had some concerns about interrupt handling cost on AST2400 BMC (ARM9), hence we did the comparison and noticed the small difference :) Cheers, Tao