From: Greg KH <gregkh@linuxfoundation.org>
To: Ivo Sieben <meltedpianoman@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>,
linux-serial@vger.kernel.org, RT <linux-rt-users@vger.kernel.org>
Subject: Re: [PATCH-v3] tty: prevent unnecessary work queue lock checking on flip buffer copy
Date: Mon, 22 Oct 2012 16:47:46 -0700 [thread overview]
Message-ID: <20121022234746.GA12743@kroah.com> (raw)
In-Reply-To: <1348747325-13539-1-git-send-email-meltedpianoman@gmail.com>
On Thu, Sep 27, 2012 at 02:02:05PM +0200, Ivo Sieben wrote:
> When low_latency flag is set the TTY receive flip buffer is copied to the
> line discipline directly instead of using a work queue in the background.
> Therefor only in case a workqueue is actually used for copying data to the
> line discipline we'll have to flush the workqueue.
>
> This prevents unnecessary spin lock/unlock on the workqueue spin lock that
> can cause additional scheduling overhead on a PREEMPT_RT system. On a 200
> MHz AT91SAM9261 processor setup this fixes about 100us of scheduling
> overhead on the TTY read call.
>
> Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com>
Note, I took out the WARN_ON() in this patch, as what is that really
going to help here? It also will conflict with a patch from Jiri I'll
ba applying after this one, so if you think it's needed, care to send a
follow-on patch based on linux-next in a few days?
thanks,
greg k-h
next prev parent reply other threads:[~2012-10-22 23:47 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-20 14:02 [PATCH] tty: prevent unnecessary work queue lock checking on flip buffer copy Ivo Sieben
2012-09-20 16:33 ` Alan Cox
2012-09-24 9:33 ` Ivo Sieben
2012-09-25 12:01 ` [PATCH-v2] " Ivo Sieben
2012-09-25 13:06 ` Alan Cox
2012-09-25 14:39 ` Ivo Sieben
2012-09-25 14:47 ` Alan Cox
2012-09-27 11:58 ` [PATCH-v3] " Ivo Sieben
2012-09-27 12:02 ` Ivo Sieben
2012-10-22 23:47 ` Greg KH [this message]
2012-10-23 10:16 ` Alan Cox
2012-10-24 12:35 ` [PATCH] [tty]: Report warning when low_latency flag is wrongly used Ivo Sieben
2012-10-24 14:32 ` Paul Gortmaker
2012-10-24 18:22 ` [PATCH-v3] tty: prevent unnecessary work queue lock checking on flip buffer copy Greg KH
2012-09-27 13:15 ` Alan Cox
2012-09-27 16:53 ` Greg KH
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