Re: [PATCH v1 1/2] tpm: msleep() delays - replace with usleep_range() in i2c nuvoton driver

[Nayna]

On 03/15/2017 09:22 PM, Jarkko Sakkinen wrote:
> 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?

Changelog v1:
>>
>> - Included Jason's feedbacks related to #defines.

Based on Jason's review:
- Added () in #define
- Replaced hardcoded maximum range value with defined name.

Hmm.. could have included exact details.

Thanks & Regards,
- Nayna

> /Jarkko