On Thu, 2017-02-23 at 17:00 -0700, Jason Gunthorpe wrote: > 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> > > drivers/char/tpm/tpm_i2c_nuvoton.c | 18 ++++++++++-------- > > 1 file changed, 10 insertions(+), 8 deletions(-) > > I wasn't aware of any of these, changes it but it makes sense to me.. > > > diff --git a/drivers/char/tpm/tpm_i2c_nuvoton.c b/drivers/char/tpm/tpm_i2c_nuvoton.c > > index e3a9155ee671..da2508a6bc0c 100644 > > +++ 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 */ > > While you are here could you put () around those #define expressions? Sure > > - msleep(TPM_I2C_BUS_DELAY); > > + usleep_range(TPM_I2C_BUS_DELAY, TPM_I2C_BUS_DELAY + 300); > > And we may as well have a constant for the 300 with a little > explanation comment that usleep_range is now required to get small > sleeps. For 250 hz, level 0 delay should be between 0 - 255ms, which is less than the 300 defined here. So before we start changing everything to use usleep_range(), I think we need to better understand what is happening. Any suggestions/recommendations would be much appreciated! Mimi
