linux-kernel - Re: [PATCH v2 2/2] livepatch: add shadow variable sample programs

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Date:   Wed, 19 Jul 2017 17:06:30 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jessica Yu <jeyu@...hat.com>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH v2 2/2] livepatch: add shadow variable sample programs

On Wed 2017-06-28 11:37:27, Joe Lawrence wrote:
> Add sample livepatch modules to demonstrate the shadow variable API.
> 
> Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
> ---
> diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
> new file mode 100644
> index 000000000000..423f4b7b0adb
> --- /dev/null
> +++ b/samples/livepatch/livepatch-shadow-mod.c
> +
> +#define T1_PERIOD 1			/* allocator thread */
> +#define T2_PERIOD (3 * T1_PERIOD)	/* cleanup thread */
> +
> +
> +	/* Dummies live long enough to see a few t2 instances */
> +	d->jiffies_expire = jiffies + 1000 * 4 * T2_PERIOD;

One more thing that I realized later. This will depend on HZ.
Also above defined periods are later multiplied by 4 or 2
so that it is not easy to understand and tune.

I would suggest to define the exact periods in ms on one
location:

#define ALLOC_PERIOD_MSEC  10
#define FREE_PERIOD_MSEC   (6 * ALLOC_PERIOD_MSEC)
#define EXPIRE_PERIOD_MSEC (24 * ALLOC_PERION_MSEC)

and then use msec_to_jiffies(XXX_PERIOD_MSEC) on
the respective locations.

Huh, I should reduce my alarm level. This is just
an example code after all.

Best Regards,
Petr