linux-kernel - Re: [PATCH v3 20/29] selftests/resctrl: Replace file write with volatile variable

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Date:   Wed, 13 Dec 2023 13:56:45 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        "Shaopeng Tan" <tan.shaopeng@...fujitsu.com>,
        Maciej Wieczór-Retman 
        <maciej.wieczor-retman@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 20/29] selftests/resctrl: Replace file write with
 volatile variable

Hi Ilpo,

On 12/11/2023 4:18 AM, Ilpo Järvinen wrote:
> The fill_buf code prevents compiler optimizating the entire read loop
> away by writing the final value of the variable into a file. While it
> achieves the goal, writing into a file requires significant amount of
> work within the innermost test loop and also error handling.
> 
> A simpler approach is to take advantage of volatile. Writing through
> a pointer to a volatile variable is enough to prevent compiler from
> optimizing the write away, and therefore compiler cannot remove the
> read loop either.
> 
> Add a volatile 'value_sink' into resctrl_tests.c and make fill_buf to
> write into it. As a result, the error handling in fill_buf.c can be
> simplified.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette