From: Andrew Morton <akpm@linux-foundation.org>
To: Timur Tabi <timur@freescale.com>
Cc: amit.shah@redhat.com, linuxppc-dev@ozlabs.org,
kumar.gala@freescale.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hvc_console: fix dropping of characters when output byte channel is full
Date: Tue, 14 Sep 2010 12:17:21 -0700 [thread overview]
Message-ID: <20100914121721.c8671ed8.akpm@linux-foundation.org> (raw)
In-Reply-To: <1282329921-24394-1-git-send-email-timur@freescale.com>
On Fri, 20 Aug 2010 13:45:21 -0500
Timur Tabi <timur@freescale.com> wrote:
> hvc_console_print() calls the HVC client driver's put_chars() callback
> to write some characters to the console. If the callback returns 0, that
> indicates that no characters were written (perhaps the output buffer is
> full), but hvc_console_print() treats that as an error and discards the
> rest of the buffer.
>
> So change hvc_console_print() to just loop and call put_chars() again if it
> returns a 0 return code.
Seems rather dangerous. The upper layer will sit there chewing 100%
CPU for as long as the lower layer is congested.
> This change makes hvc_console_print() behave more like hvc_push(), which
> does check for a 0 return code and re-schedules itself.
Yes, hvc_push() reschedules. It doesn't sit in a tight loop burning
electrons!
Can we do something safer&smarter here?
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Timur Tabi <timur@freescale.com>
Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
benh@kernel.crashing.org, kumar.gala@freescale.com,
amit.shah@redhat.com
Subject: Re: [PATCH] hvc_console: fix dropping of characters when output byte channel is full
Date: Tue, 14 Sep 2010 12:17:21 -0700 [thread overview]
Message-ID: <20100914121721.c8671ed8.akpm@linux-foundation.org> (raw)
In-Reply-To: <1282329921-24394-1-git-send-email-timur@freescale.com>
On Fri, 20 Aug 2010 13:45:21 -0500
Timur Tabi <timur@freescale.com> wrote:
> hvc_console_print() calls the HVC client driver's put_chars() callback
> to write some characters to the console. If the callback returns 0, that
> indicates that no characters were written (perhaps the output buffer is
> full), but hvc_console_print() treats that as an error and discards the
> rest of the buffer.
>
> So change hvc_console_print() to just loop and call put_chars() again if it
> returns a 0 return code.
Seems rather dangerous. The upper layer will sit there chewing 100%
CPU for as long as the lower layer is congested.
> This change makes hvc_console_print() behave more like hvc_push(), which
> does check for a 0 return code and re-schedules itself.
Yes, hvc_push() reschedules. It doesn't sit in a tight loop burning
electrons!
Can we do something safer&smarter here?
next prev parent reply other threads:[~2010-09-14 19:17 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-20 18:45 [PATCH] hvc_console: fix dropping of characters when output byte channel is full Timur Tabi
2010-09-14 16:05 ` Timur Tabi
2010-09-14 16:05 ` Timur Tabi
2010-09-14 19:17 ` Andrew Morton [this message]
2010-09-14 19:17 ` Andrew Morton
2010-09-14 19:22 ` Scott Wood
2010-09-14 19:22 ` Scott Wood
2010-09-14 19:44 ` Alan Cox
2010-09-14 19:44 ` Alan Cox
2010-09-14 19:25 ` Timur Tabi
2010-09-14 19:25 ` Timur Tabi
2010-09-14 19:52 ` Alan Cox
2010-09-14 19:52 ` Alan Cox
2010-09-14 19:44 ` Timur Tabi
2010-09-14 19:44 ` Timur Tabi
2010-09-14 20:05 ` Scott Wood
2010-09-14 20:05 ` Scott Wood
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100914121721.c8671ed8.akpm@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=amit.shah@redhat.com \
--cc=kumar.gala@freescale.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@ozlabs.org \
--cc=timur@freescale.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.