linux-kernel - Re: [PATCH 3/4] tty: omap-serial: use threaded interrupt handler

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <54197804.3020302@hurleysoftware.com>
Date:	Wed, 17 Sep 2014 08:01:08 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Frans Klaver <frans.klaver@...ns.com>
CC:	Tony Lindgren <tony@...mide.com>, Felipe Balbi <balbi@...com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexey Pelykh <alexey.pelykh@...il.com>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] tty: omap-serial: use threaded interrupt handler

On 09/16/2014 04:50 AM, Frans Klaver wrote:
> On Mon, Sep 15, 2014 at 01:31:56PM -0400, Peter Hurley wrote:
>> On 09/15/2014 11:39 AM, Peter Hurley wrote:
>>> On 09/15/2014 10:00 AM, Frans Klaver wrote:
>>>> At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
>>>> rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
>>>> this to about 170 overflows in 10 minutes.
>>>
>>> Why is the threadirqs kernel boot option not sufficient?
>>> Or conversely, shouldn't this be selectable?
>>
> 
> I wasn't aware of the threadirqs boot option. I also wouldn't know if
> this should be selectable. What would be a reason to favor the
> non-threaded irq over the threaded irq?

Not everyone cares enough about serial to dedicate kthreads to it :)

>> Also, do you see the same performance differential when you implement this
>> in the 8250 driver (that is, on top of Sebastian's omap->8250 conversion)?
>>
> 
> I haven't gotten Sebastian's driver to work properly yet on the console.
> There was no reason for me yet to throw my omap changes on top of
> Sebastian's queue.
> 
>>> PS - To overflow the 64 byte RX FIFO at those data rates means interrupt
>>> latency in excess of 250us?
> 
> At 3686400 baud it should take about 174 us to fill a 64 byte buffer. I
> haven't done any measurements on the interrupt latency though. If you
> consider that we're sending about 1kB of data, 240 times a second, we're
> spending a lot of time reading data from the uart. I can imagine the
> system has other work to do as well.

System work should not keep irqs from being serviced. Even 174us is a long
time not to service an interrupt. Maybe console writes are keeping the isr
from running?

Regards,
Peter Hurley

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/