linux-kernel - RE: [PATCH 04/11] Blackfin SPORT UART: fix overrun errors

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Date:	Wed, 3 Jun 2009 16:49:41 +0800
From:	"Cai, Cliff" <Cliff.Cai@...log.com>
To:	"Mike Frysinger" <vapier.adi@...il.com>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>
CC:	"Mike Frysinger" <vapier@...too.org>,
	<linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<uclinux-dist-devel@...ckfin.uclinux.org>,
	"Bryan Wu" <cooloney@...nel.org>
Subject: RE: [PATCH 04/11] Blackfin SPORT UART: fix overrun errors

 

>-----Original Message-----
>From: Mike Frysinger [mailto:vapier.adi@...il.com] 
>Sent: Wednesday, June 03, 2009 4:04 PM
>To: Alan Cox
>Cc: Mike Frysinger; linux-serial@...r.kernel.org; 
>linux-kernel@...r.kernel.org; 
>uclinux-dist-devel@...ckfin.uclinux.org; Cai, Cliff; Bryan Wu
>Subject: Re: [PATCH 04/11] Blackfin SPORT UART: fix overrun errors
>
>On Tue, Jun 2, 2009 at 05:00, Alan Cox wrote:
>> On Tue,  2 Jun 2009 03:11:33 -0400 Mike Frysinger wrote:
>>> From: Cliff Cai <cliff.cai@...log.com>
>>>
>>> Push the ty_flip_buffer_push() call from the IRQ handler to a timer 
>>> so as to improve performance and decrease likelihood of overruns.
>>
>> This should have no effect on a modern kernel.
>
>well, we wouldnt be making changes if we werent seeing data 
>overruns today
>
>> There is 64K of queueing between you and the ldisc nowdays.
>
>i dont think that really matters ... we do too much work in 
>the interrupt and so we miss new data
>
>> Furthermore unless you set tty->low_latency the kernel already 
>> basically does this aggregation for you as the buffer push queues 
>> stuff for the ldisc to wake up and process.
>
>i guess we could try setting the low_latency bool instead and 
>see if that fixes things -mike
>

The overrrun problem doesn't exist even without my patch now,so I will drop it.

Thanks

Cliff
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