RE: [PATCH v2 2/7] HID: ft260: improve i2c write performance

[David Laight <David.Laight@ACULAB.COM>]

From: Michael Zaidman
> Sent: 28 September 2022 15:49
> 
> The patch improves i2c writing performance by about 30 percent by revising
> the sleep time in the ft260_hid_output_report_check_status() in the
> following ways:

Spinning in kernel for several milliseconds isn't friendly at all.

	David

> 
> 1. Reduce the sleep time and start to poll earlier:
> 
>   Before:
>     $ sudo ./i2cperf -f 2 -o 2 -s 32 -r 0-0xff 13 0x51 -S
> 
>       Fill block with increment via i2ctransfer by chunks
>       -------------------------------------------------------------------
>       data rate(bps)  efficiency(%)  data size(B)  total IOs   IO size(B)
>       -------------------------------------------------------------------
>       40510           80             256           8           32
> 
>   After:
>     $ sudo ./i2cperf -f 2 -o 2 -s 32 -r 0-0xff 13 0x51 -S
> 
>       Fill block with increment via i2ctransfer by chunks
>       -------------------------------------------------------------------
>       data rate(bps)  efficiency(%)  data size(B)  total IOs   IO size(B)
>       -------------------------------------------------------------------
>       52584           80             256           8           32
> 
> 2. Do not sleep when the calculated sleep time is below 2 ms:
> 
>   Before:
>     $ sudo ./i2cperf -f 2 -o 2 -s 16 -r 0-0xff 13 0x51 -S
> 
>       Fill block with increment via i2ctransfer by chunks
>       -------------------------------------------------------------------
>       data rate(bps)  efficiency(%)  data size(B)  total IOs   IO size(B)
>       -------------------------------------------------------------------
>       26707           73             256           16          16
> 
>   After:
>     $ sudo ./i2cperf -f 2 -o 2 -s 16 -r 0-0xff 13 0x51 -S
> 
>       Fill block with increment via i2ctransfer by chunks
>       -------------------------------------------------------------------
>       data rate(bps)  efficiency(%)  data size(B)  total IOs   IO size(B)
>       -------------------------------------------------------------------
>       37034           73             256           16          16
> 
> Link to the i2cperf - https://github.com/MichaelZaidman/i2cperf
> 
> Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
> Tested-by: Guillaume Champagne <champagne.guillaume.c@gmail.com>
> ---
>  drivers/hid/hid-ft260.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
> index a35201d68b15..44106cadd746 100644
> --- a/drivers/hid/hid-ft260.c
> +++ b/drivers/hid/hid-ft260.c
> @@ -345,7 +345,7 @@ static int ft260_hid_output_report(struct hid_device *hdev, u8 *data,
>  static int ft260_hid_output_report_check_status(struct ft260_device *dev,
>  						u8 *data, int len)
>  {
> -	int ret, usec, try = 3;
> +	int ret, usec, try = 100;
>  	struct hid_device *hdev = dev->hdev;
> 
>  	ret = ft260_hid_output_report(hdev, data, len);
> @@ -356,10 +356,14 @@ static int ft260_hid_output_report_check_status(struct ft260_device *dev,
>  		return ret;
>  	}
> 
> -	/* transfer time = 1 / clock(KHz) * 10 bits * bytes */
> -	usec = 10000 / dev->clock * len;
> -	usleep_range(usec, usec + 100);
> -	ft260_dbg("wait %d usec, len %d\n", usec, len);
> +	/* transfer time = 1 / clock(KHz) * 9 bits * bytes */
> +	usec = len * 9000 / dev->clock;
> +	if (usec > 2000) {
> +		usec -= 1500;
> +		usleep_range(usec, usec + 100);
> +		ft260_dbg("wait %d usec, len %d\n", usec, len);
> +	}
> +
>  	do {
>  		ret = ft260_xfer_status(dev);
>  		if (ret != -EAGAIN)
> --
> 2.34.1

-
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