linux-kernel - Re: [PATCH] serial: imx: reduce irq-latency after rx overflow

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Message-ID: <4275820.CIOTxUBfmF@ws-stein>
Date:	Mon, 22 Jun 2015 08:48:44 +0200
From:	Alexander Stein <alexander.stein@...tec-electronic.com>
To:	Manfred Schlaegl <manfred.schlaegl@....at>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Manfred Schlaegl <manfred.schlaegl@...zinger.com>
Subject: Re: [PATCH] serial: imx: reduce irq-latency after rx overflow

Am Samstag, 20. Juni 2015, 19:25:52 schrieb Manfred Schlaegl:
> To prevent problems with interrupt latency, and due to the fact, that
> the error will be counted anyway (icount.overrun), the dev_err is simply
> removed.
> 
> Background:
> If an rx-fifo overflow occurs a dev_err message was called in interrupt
> context. Since dev_err messages are written to console in a synchronous way
> (unbuffered), and console may be a serial terminal, this leads to a
> highly increased interrupt-latency (several milliseconds).
> As a result of the high latency more rx-fifo overflows will happen, and
> therefore a feedback loop of errors is created.

I understand your rationale but removing this error message from kernel log removes the possibility to detect serial overruns by simply check the kernel log or output on kernel console. AFAICS you have to use TIOCGICOUNT to get the error counters.
How about introducing a rate limit for this kernel message?

Best regards,
Alexander
-- 
Dipl.-Inf. Alexander Stein

SYS TEC electronic GmbH
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