From: Alexander Stein <alexander.stein@systec-electronic.com>
To: David Jander <david@protonic.nl>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>,
Wolfgang Grandegger <wg@grandegger.com>,
linux-can@vger.kernel.org
Subject: Re: [PATCH v5] can: flexcan: Re-write receive path to use MB queue instead of FIFO
Date: Tue, 30 Sep 2014 09:43:33 +0200 [thread overview]
Message-ID: <2928841.hvxjaQ0ECy@ws-stein> (raw)
In-Reply-To: <20140930091355.770fac72@archvile>
Hello David,
On Tuesday 30 September 2014 09:13:55, David Jander wrote:
> > > Nevertheless, emptying the FIFO in the IRQ handler will still be a big
> > > improvement, since the only thing that could still kill the driver and
> > > cause message loss is interrupt latency, which normally should not be so
> > > high. NAPI scheduling latency is probably much worse, and this is the
> > > biggest issue with the current driver.
> > >
> > > Any suggestion on what to do?
> >
> > Get rid of NAPI and use RT-preempt with proper priorities :) But joke aside,
> > which workload does increase the NAPI latency so much, an overrun occurs? I
> > tested CAN bursts on i.MX35 without any loss.
>
> I have seen overruns on an i.MX6 at only 250kbaud receiving back-to-back
> messages of 1 byte long. I usually test bursts of 10000 messages or more.
Mh, that's odd. I have run several tests a 1MBaud on an i.MX35 with 2 CAN nodes attached each sending bursts of 250 message every 200ms with a total message count of 250000 each. No overruns, losses or message misordering.
> Things get a lot worse if you also happen to have kernel messages output to a
> serial console and plug in an USB device (because there are printk's in the
> EHCI driver inside spin locks with interrupts disabled!!), but that's a
> different story.
Eek. Well, adding quiet to the command line avoids that. IIRC there is even a Kconfig option to disable that announce to kernel log.
Best regards,
Alexander
--
Dipl.-Inf. Alexander Stein
SYS TEC electronic GmbH
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next prev parent reply other threads:[~2014-09-30 7:42 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-29 12:52 [PATCH v5] can: flexcan: Re-write receive path to use MB queue instead of FIFO David Jander
2014-09-29 13:29 ` Alexander Stein
2014-09-29 14:39 ` David Jander
2014-09-29 15:02 ` Alexander Stein
2014-09-30 7:13 ` David Jander
2014-09-30 7:43 ` Alexander Stein [this message]
2014-10-01 6:29 ` David Jander
2014-10-01 7:11 ` Alexander Stein
2014-10-01 7:15 ` Marc Kleine-Budde
2014-10-01 8:29 ` Alexander Stein
2014-10-01 9:07 ` David Jander
2014-10-01 9:19 ` Alexander Stein
2014-10-01 9:34 ` David Jander
2014-10-01 9:58 ` Marc Kleine-Budde
2014-10-06 7:28 ` David Jander
2014-10-06 10:00 ` Marc Kleine-Budde
2014-10-06 11:17 ` David Jander
2014-10-07 9:30 ` [RFC PATCH 1/2] can: rx-fifo: Increase MB size limit from 32 to 64 David Jander
2014-10-07 9:30 ` [RFC PATCH 2/2] can: rx-fifo: Add support for IRQ readout and NAPI poll David Jander
2014-10-07 13:17 ` [RFC PATCH 1/2] can: rx-fifo: Increase MB size limit from 32 to 64 Marc Kleine-Budde
2014-10-07 13:27 ` David Jander
2014-10-07 14:18 ` Marc Kleine-Budde
2014-10-08 9:08 ` [PATCH v5] can: flexcan: Re-write receive path to use MB queue instead of FIFO David Jander
2014-10-08 9:56 ` Marc Kleine-Budde
2014-10-08 10:36 ` Alexander Stein
2014-10-08 10:43 ` Marc Kleine-Budde
2014-10-08 14:01 ` David Jander
2014-10-09 10:37 ` David Jander
2014-10-01 9:19 ` David Jander
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