From: David Laight <David.Laight@ACULAB.COM>
To: "'Wander Lairson Costa'" <wander@redhat.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Jiri Slaby" <jirislaby@kernel.org>,
"Johan Hovold" <johan@kernel.org>,
"Maciej W. Rozycki" <macro@orcam.me.uk>,
"Serge Semin" <fancer.lancer@gmail.com>,
"Lukas Wunner" <lukas@wunner.de>, "Pali Rohár" <pali@kernel.org>,
"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
"open list" <linux-kernel@vger.kernel.org>
Cc: "rostedt@goodmis.org" <rostedt@goodmis.org>,
"senozhatsky@chromium.org" <senozhatsky@chromium.org>,
"andre.goddard@gmail.com" <andre.goddard@gmail.com>,
"sudipm.mukherjee@gmail.com" <sudipm.mukherjee@gmail.com>,
"andy.shevchenko@gmail.com" <andy.shevchenko@gmail.com>,
"jonathanh@nvidia.com" <jonathanh@nvidia.com>,
"phil@raspberrypi.com" <phil@raspberrypi.com>
Subject: RE: [PATCH v4 1/5] serial/8250: Use fifo in 8250 console driver
Date: Wed, 16 Mar 2022 15:27:26 +0000 [thread overview]
Message-ID: <bb5f03ec092f462c9656f224895bb224@AcuMS.aculab.com> (raw)
In-Reply-To: <20220316143646.13301-2-wander@redhat.com>
From: Wander Lairson Costa
> Sent: 16 March 2022 14:37
>
> Note: I am using a small test app + driver located at [0] for the
> problem description. serco is a driver whose write function dispatches
> to the serial controller. sertest is a user-mode app that writes n bytes
> to the serial console using the serco driver.
>
> While investigating a bug in the RHEL kernel, I noticed that the serial
> console throughput is way below the configured speed of 115200 bps in
> a HP Proliant DL380 Gen9. I was expecting something above 10KB/s, but
> I got 2.5KB/s.
>
> $ time ./sertest -n 2500 /tmp/serco
>
> real 0m0.997s
> user 0m0.000s
> sys 0m0.997s
>
> With the help of the function tracer, I then noticed the serial
> controller was taking around 410us seconds to dispatch one single byte:
Did you verify the baud rate?
Or is there some horrid serial redirection going on.
It is even possible there is a bios smm interrupt
chugging through on another cpu core.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-03-16 15:27 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-16 14:36 [PATCH v4 0/5] tty/8250: Use fifo in 8250 console driver Wander Lairson Costa
2022-03-16 14:36 ` [PATCH v4 1/5] serial/8250: " Wander Lairson Costa
2022-03-16 15:27 ` David Laight [this message]
2022-03-17 12:27 ` Wander Costa
2022-03-16 14:36 ` [PATCH v4 2/5] serial/8250: Use the cache value of the FCR register Wander Lairson Costa
2022-03-17 8:29 ` Ilpo Järvinen
2022-03-17 12:03 ` Wander Costa
2022-03-16 14:36 ` [PATCH v4 3/5] serial/8250: Use tx_loadsz as the transmitter fifo size Wander Lairson Costa
2022-03-16 14:36 ` [PATCH v4 4/5] serial/8250: exclude BCM283x from console_fifo_write Wander Lairson Costa
2022-03-16 14:36 ` [PATCH v4 5/5] serial/8250: Only use fifo after the port is initialized in console_write Wander Lairson Costa
2022-03-17 7:06 ` Jiri Slaby
2022-03-17 12:22 ` Wander Costa
2022-03-17 8:43 ` Ilpo Järvinen
2022-03-17 12:23 ` Wander Costa
2022-03-16 16:13 ` [PATCH v4 0/5] tty/8250: Use fifo in 8250 console driver Andy Shevchenko
2022-03-16 16:14 ` Andy Shevchenko
2022-03-16 16:37 ` Wander Costa
2022-03-17 15:47 ` Steven Rostedt
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