On Thu, Feb 23, 2017 at 06:46:18PM -0500, Mimi Zohar wrote:
> Commit 500462a9de65 "timers: Switch to a non-cascading wheel" replaced
> the 'classic' timer wheel, which aimed for near 'exact' expiry of the
> timers. Their analysis was that the vast majority of timeout timers
> are used as safeguards, not as real timers, and are cancelled or
> rearmed before expiration. The only exception noted to this were
> networking timers with a small expiry time.
>
> Not included in the analysis was the TPM polling timer, which resulted
> in a longer normal delay and, every so often, a very long delay. The
> non-cascading wheel delay is based on CONFIG_HZ. For a description of
> the different rings and their delays, refer to the comments in
> kernel/time/timer.c.
>
> Below are the delays given for rings 0 - 2, which explains the longer
> "normal" delays and the very, long delays as seen on systems with
> CONFIG_HZ 250.
>
> * HZ 1000 steps
> * Level Offset Granularity Range
> * 0 0 1 ms 0 ms - 63 ms
> * 1 64 8 ms 64 ms - 511 ms
> * 2 128 64 ms 512 ms - 4095 ms (512ms - ~4s)
>
> * HZ 250
> * Level Offset Granularity Range
> * 0 0 4 ms 0 ms - 255 ms
> * 1 64 32 ms 256 ms - 2047 ms (256ms - ~2s)
> * 2 128 256 ms 2048 ms - 16383 ms (~2s - ~16s)
>
> Below is a comparison of extending the TPM with 1000 measurements,
> using msleep() vs. usleep_delay() when configured for 1000 hz vs. 250
> hz, before and after commit 500462a9de65.
>
> linux-4.7 | msleep() usleep_range()
> 1000 hz: 0m44.628s | 1m34.497s 29.243s
> 250 hz: 1m28.510s | 4m49.269s 32.386s
>
> linux-4.7 | min-max (msleep) min-max (usleep_range)
> 1000 hz: 0:017 - 2:760s | 0:015 - 3:967s 0:014 - 0:418s
> 250 hz: 0:028 - 1:954s | 0:040 - 4:096s 0:016 - 0:816s
>
> This patch replaces the msleep() with usleep_range() calls in the
> i2c nuvoton driver with a consistent max range value.
>
> Signed-of-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
So why doesn't it go to level 0 with msleep()? I quickly skimmed
through __mod_timer() and for me it looked like that level 0 would be
calculated (when it is eventually called starting from msleep()).
What did I miss?
/Jarkko
> ---
> drivers/char/tpm/tpm_i2c_nuvoton.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_i2c_nuvoton.c b/drivers/char/tpm/tpm_i2c_nuvoton.c
> index e3a9155ee671..da2508a6bc0c 100644
> --- a/drivers/char/tpm/tpm_i2c_nuvoton.c
> +++ b/drivers/char/tpm/tpm_i2c_nuvoton.c
> @@ -49,9 +49,9 @@
> */
> #define TPM_I2C_MAX_BUF_SIZE 32
> #define TPM_I2C_RETRY_COUNT 32
> -#define TPM_I2C_BUS_DELAY 1 /* msec */
> -#define TPM_I2C_RETRY_DELAY_SHORT 2 /* msec */
> -#define TPM_I2C_RETRY_DELAY_LONG 10 /* msec */
> +#define TPM_I2C_BUS_DELAY 1000 /* usec */
> +#define TPM_I2C_RETRY_DELAY_SHORT 2 * 1000 /* usec */
> +#define TPM_I2C_RETRY_DELAY_LONG 10 * 1000 /* usec */
>
> #define OF_IS_TPM2 ((void *)1)
> #define I2C_IS_TPM2 1
> @@ -123,7 +123,7 @@ static s32 i2c_nuvoton_write_status(struct i2c_client *client, u8 data)
> /* this causes the current command to be aborted */
> for (i = 0, status = -1; i < TPM_I2C_RETRY_COUNT && status < 0; i++) {
> status = i2c_nuvoton_write_buf(client, TPM_STS, 1, &data);
> - msleep(TPM_I2C_BUS_DELAY);
> + usleep_range(TPM_I2C_BUS_DELAY, TPM_I2C_BUS_DELAY + 300);
> }
> return status;
> }
> @@ -160,7 +160,7 @@ static int i2c_nuvoton_get_burstcount(struct i2c_client *client,
> burst_count = min_t(u8, TPM_I2C_MAX_BUF_SIZE, data);
> break;
> }
> - msleep(TPM_I2C_BUS_DELAY);
> + usleep_range(TPM_I2C_BUS_DELAY, TPM_I2C_BUS_DELAY + 300);
> } while (time_before(jiffies, stop));
>
> return burst_count;
> @@ -203,13 +203,15 @@ static int i2c_nuvoton_wait_for_stat(struct tpm_chip *chip, u8 mask, u8 value,
> return 0;
>
> /* use polling to wait for the event */
> - ten_msec = jiffies + msecs_to_jiffies(TPM_I2C_RETRY_DELAY_LONG);
> + ten_msec = jiffies + usecs_to_jiffies(TPM_I2C_RETRY_DELAY_LONG);
> stop = jiffies + timeout;
> do {
> if (time_before(jiffies, ten_msec))
> - msleep(TPM_I2C_RETRY_DELAY_SHORT);
> + usleep_range(TPM_I2C_RETRY_DELAY_SHORT,
> + TPM_I2C_RETRY_DELAY_SHORT + 300);
> else
> - msleep(TPM_I2C_RETRY_DELAY_LONG);
> + usleep_range(TPM_I2C_RETRY_DELAY_LONG,
> + TPM_I2C_RETRY_DELAY_LONG + 300);
> status_valid = i2c_nuvoton_check_status(chip, mask,
> value);
> if (status_valid)
> --
> 2.9.3
>
>
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