[PATCH v3] console: usb: kbd: Limit poll frequency to improve performance

Thomas Watson twatson52 at icloud.com
Fri Feb 11 02:43:02 CET 2022

> On Feb 10, 2022, at 5:04 PM, Marek Vasut <marex at denx.de> wrote:
> On 2/11/22 00:02, Simon Glass wrote:
>> Hi Marek,
>> 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?
> Since there are multiple instances of the ifdef already , subsequent patch to clean them up would be fine.

That function `state_get_skip_delays()` and that state.h header file in general
is only defined in the sandbox architecture, so I don't think it's possible to
remove the #ifdef unless that is changed.

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