Re: [PATCH v1 1/2] tpm: msleep() delays - replace with usleep_range() in i2c nuvoton driver
From: Jarkko Sakkinen
Date: Wed Mar 15 2017 - 11:53:41 EST
On Fri, Mar 10, 2017 at 01:45:53PM -0500, Nayna Jain 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>
> Cc: stable@xxxxxxxxxxxxxxx (linux-4.8)
> Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
> ---
> Changelog v1:
>
> - Included Jason's feedbacks related to #defines.
What was changed?
/Jarkko