Commit 500462a9de "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 500462a9de.
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@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org (linux-4.8)
Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
a233a0289c