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Date: Tue, 7 Jul 2015 11:10:29 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: "Gaohaifeng (A)" <gaohaifeng.gao@huawei.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stephan.baerwolf@tu-ilmenau.de" <stephan.baerwolf@tu-ilmenau.de>,
        "Huangjian (J)" <huangjian.huangjian@huawei.com>
Subject: Re: sched:  about vruntime overflow
Message-ID: <20150707091029.GP3644@twins.programming.kicks-ass.net>
References: <47CEA9C0E570484FBF22EF0D7EBCE5B534B17A98@szxema505-mbs.china.huawei.com>
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On Tue, Jul 07, 2015 at 08:05:50AM +0000, Gaohaifeng (A) wrote:
> int main()
> {
>         unsigned char a,b;
>         a=251;
>         b=254;
>         b +=5;  // b will overflow
>         printf("a=%u \n",a);
>         printf("b=%u \n",b);
>         printf("(a-b<0)=%d\n",(a-b)<0);

If you look at entity_before() you'll notice that the correct statement
would be:

	printf("(a-b<0)=%d\n",(signed char)(a-b)<0);

>         printf("(a-b<0)=%d\n",((unsigned char)(a-250)-(unsigned char)(b-250)<0));
>         return 0;
> }