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Date:   Mon, 14 Sep 2020 12:41:11 +0100
From:   Qais Yousef <qais.yousef@arm.com>
To:     John Dias <joaodias@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>, qianjun.kernel@gmail.com,
        tglx@linutronix.de, will@kernel.org, luto@kernel.org,
        LKML <linux-kernel@vger.kernel.org>, laoar.shao@gmail.com,
        urezki@gmail.com, Wei Wang <wvw@google.com>,
        Quentin Perret <qperret@google.com>
Subject: Re: [PATCH V6 1/1] Softirq:avoid large sched delay from the pending
 softirqs
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On 09/11/20 12:14, John Dias wrote:
> I agree that the rt-softirq interaction patches are a gross hack (and I
> wrote the original versions, so it's my grossness). The problem is that
> even a 1ms delay in executing those low-latency audio threads is enough to
> cause obvious glitching in audio under very real circumstances, which is
> not an acceptable user experience -- and some softirq handlers run for >1ms
> on their own. (And 1ms is a high upper bound, not a median target.)

AFAIK professional audio apps have the toughest limit of sub 10ms. 120MHz
screens impose a stricter limit on display pipeline too to finish its frame in
8ms.

1ms is too short and approaches PREEMPT_RT realm.

Is it possible to expand on the use case here? What application requires this
constraint?

Thanks

--
Qais Yousef