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