linux-kernel - Re: [PATCH v1 1/2] tpm: msleep() delays - replace with usleep

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Message-ID: <20170315155226.xtgpttv5slej77ep@intel.com>
Date:   Wed, 15 Mar 2017 17:52:26 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Nayna Jain <nayna@...ux.vnet.ibm.com>
Cc:     tpmdd-devel@...ts.sourceforge.net, peterhuewe@....de,
        tpmdd@...horst.net, jgunthorpe@...idianresearch.com,
        dan.morav@...oton.com, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, "linux-4.8" <stable@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] tpm: msleep() delays - replace with
 usleep_range() in i2c nuvoton driver

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@...ux.vnet.ibm.com>
> Cc: stable@...r.kernel.org (linux-4.8)
> Signed-off-by: Nayna Jain <nayna@...ux.vnet.ibm.com>
> ---
> Changelog v1:
> 
> - Included Jason's feedbacks related to #defines.

What was changed?

/Jarkko