[PATCH v3] console: usb: kbd: Limit poll frequency to improve performance
sjg at chromium.org
Fri Feb 11 00:02:07 CET 2022
On Thu, 10 Feb 2022 at 14:42, Marek Vasut <marex at denx.de> wrote:
> On 2/10/22 22:13, Thomas Watson wrote:
> > Using the XHCI driver, the function `usb_kbd_poll_for_event` takes
> > 30-40ms to run. The exact time is dependent on the polling interval the
> > keyboard requests in its descriptor, and likely cannot be significantly
> > reduced without major rework to the XHCI driver.
> > The U-Boot EFI console service sets a timer to poll the keyboard every 5
> > microseconds, and this timer is checked every time a block is read off
> > disk. The net effect is that, on my system, loading a ~40MiB kernel and
> > initrd takes about 62 seconds with a slower keyboard and 53 seconds
> > with a faster one, with the vast majority of the time spent polling the
> > keyboard.
> > To solve this problem, this patch adds a 20ms delay between consecutive
> > calls to `usb_kbd_poll_for_event`. This is sufficient to reduce the
> > total loading time to under half a second for both keyboards, and does
> > not impact the perceived keystroke latency.
> > Signed-off-by: Thomas Watson <twatson52 at icloud.com>
> > ---
> > This revision fixes a sandbox test failure by honoring the test's
> > request to skip delays.
> > common/usb_kbd.c | 31 ++++++++++++++++++++++++++-----
> > 1 file changed, 26 insertions(+), 5 deletions(-)
We don't want to delay the CI tests which take enough time as it is.
So time needs to be faked.
It could be an if() though, rather than #if, perhaps?
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