From: Alan Cox <alan@linux.intel.com>
To: Ivo Sieben <meltedpianoman@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
linux-serial@vger.kernel.org, RT <linux-rt-users@vger.kernel.org>
Subject: Re: [PATCH] tty: prevent unnecessary work queue lock checking on flip buffer copy
Date: Thu, 20 Sep 2012 17:33:05 +0100 [thread overview]
Message-ID: <20120920173305.15ea580a@bob.linux.org.uk> (raw)
In-Reply-To: <1348149762-4596-1-git-send-email-meltedpianoman@gmail.com>
> This prevents unnecessary spin lock/unlock on the workqueue spin lock
> that can cause additional scheduling overhead on a PREEMPT_RT system.
> On a 240 MHz AT91SAM9261 processor setup this fixes about 100us of
> scheduling overhead on the TTY read call.
This seems reasonable, but given its also relevant for upstream it
would be nice to get it without the ifdef in upstream.
The corner case is when the tty->low_latency flag is flipped but the
drivers should handle that gracefully and if not we should fix them so
you can get your 100uS.
Alan
WARNING: multiple messages have this Message-ID (diff)
From: Alan Cox <alan@linux.intel.com>
To: Ivo Sieben <meltedpianoman@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
<linux-serial@vger.kernel.org>,
RT <linux-rt-users@vger.kernel.org>
Subject: Re: [PATCH] tty: prevent unnecessary work queue lock checking on flip buffer copy
Date: Thu, 20 Sep 2012 17:33:05 +0100 [thread overview]
Message-ID: <20120920173305.15ea580a@bob.linux.org.uk> (raw)
In-Reply-To: <1348149762-4596-1-git-send-email-meltedpianoman@gmail.com>
> This prevents unnecessary spin lock/unlock on the workqueue spin lock
> that can cause additional scheduling overhead on a PREEMPT_RT system.
> On a 240 MHz AT91SAM9261 processor setup this fixes about 100us of
> scheduling overhead on the TTY read call.
This seems reasonable, but given its also relevant for upstream it
would be nice to get it without the ifdef in upstream.
The corner case is when the tty->low_latency flag is flipped but the
drivers should handle that gracefully and if not we should fix them so
you can get your 100uS.
Alan
next prev parent reply other threads:[~2012-09-20 16:14 UTC|newest]
Thread overview: 25+ 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 14:02 ` Ivo Sieben
2012-09-20 16:33 ` Alan Cox [this message]
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 12:01 ` Ivo Sieben
2012-09-25 13:06 ` Alan Cox
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 11:58 ` Ivo Sieben
2012-09-27 12:02 ` 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 12:35 ` Ivo Sieben
2012-10-24 14:32 ` Paul Gortmaker
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 13:15 ` Alan Cox
2012-09-27 16:53 ` Greg KH
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