From: Greg KH <gregkh@linuxfoundation.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Ivo Sieben <meltedpianoman@gmail.com>,
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: Thu, 27 Sep 2012 09:53:53 -0700 [thread overview]
Message-ID: <20120927165353.GA20469@kroah.com> (raw)
In-Reply-To: <20120927141522.7d3e26de@pyramind.ukuu.org.uk>
On Thu, Sep 27, 2012 at 02:15:22PM +0100, Alan Cox wrote:
> On Thu, 27 Sep 2012 13:58:21 +0200
> Ivo Sieben <meltedpianoman@gmail.com> 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>
>
> Acked-by: Alan Cox <alan@linux.intel.com>
>
> (but for 3.8 not 3.7 ...)
Yes, I will hold onto this until 3.7-rc1 is out, thanks.
greg k-h
prev parent reply other threads:[~2012-09-27 16:53 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
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 [this message]
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