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From:   Thomas Gleixner <tglx@linutronix.de>
To:     qianjun.kernel@gmail.com, peterz@infradead.org, will@kernel.org,
        luto@kernel.org, linux-kernel@vger.kernel.org, urezki@gmail.com
Cc:     laoar.shao@gmail.com, jun qian <qianjun.kernel@gmail.com>
Subject: Re: [RFC PATCH v2] Softirq:avoid large sched delay from the pending softirqs
In-Reply-To: <1595250506-9769-1-git-send-email-qianjun.kernel@gmail.com>
References: <1595250506-9769-1-git-send-email-qianjun.kernel@gmail.com>
Date:   Wed, 22 Jul 2020 20:05:22 +0200
Message-ID: <87eep32zod.fsf@nanos.tec.linutronix.de>
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qianjun.kernel@gmail.com writes:
> +
> +		end = ktime_get();
> +		delta = ktime_to_us(end - start);

What's the point of this conversion? That's a division for no value
because you can simply define the maximum time in nanoseconds with the
same effect, i.e.

	ktime_t end = ktime_get() + MAX_SOFTIRQ_TIME_NS;

	if (need_resched() && ktime_get() > end)
		break;

So you can spare all that start, delta and conversion dance and keep the
code simple.

Also notice that need_resched() wants to be evaluated first because
there is no point to do the more expensive time read if need_resched()
is false.

Thanks,

        tglx