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Message-ID: <6358c720-66a9-4727-a74d-b56100f01ac4@intel.com>
Date:   Tue, 28 Nov 2023 14:16:28 -0800
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Subject: Re: [PATCH v2 17/26] selftests/resctrl: Replace file write with
 volatile variable
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To:     =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        <linux-kselftest@vger.kernel.org>, Shuah Khan <shuah@kernel.org>,
        "Shaopeng Tan" <tan.shaopeng@jp.fujitsu.com>,
        =?UTF-8?Q?Maciej_Wiecz=C3=B3r-Retman?= 
        <maciej.wieczor-retman@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>
CC:     <linux-kernel@vger.kernel.org>
References: <20231120111340.7805-1-ilpo.jarvinen@linux.intel.com>
 <20231120111340.7805-18-ilpo.jarvinen@linux.intel.com>
From:   Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <20231120111340.7805-18-ilpo.jarvinen@linux.intel.com>
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Hi Ilpo,

On 11/20/2023 3:13 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 to a
> variable through a volatile pointer 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.
> 

The subject and changelog describes the need for a volatile variable.
The patch introduces two volatile variables. Could you please elaborate
why two volatile variables are needed?

Reinette