linux-kernel - Re: AIM7 40% regression with 2.6.26-rc1

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Message-ID: <20080507062834.GA30306@elte.hu>
Date:	Wed, 7 May 2008 08:28:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Matthew Wilcox <matthew@....cx>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@....linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: AIM7 40% regression with 2.6.26-rc1


* Ingo Molnar <mingo@...e.hu> wrote:

> > 3) Caller of lock_kernel are sys_fcntl/vfs_ioctl/tty_release/chrdev_open.
> 
> that's one often-forgotten BKL site: about 1000 ioctls are still 
> running under the BKL. The TTY one is hurting the most. [...]

although it's an unlocked_ioctl() now in 2.6.26, so all the BKL locking 
has been nicely pushed down to deep inside the tty code.

> [...] To make sure it's only that BKL acquire/release that hurts, 
> could you try the hack patch below, does it make any difference to 
> performance?

if you use a serial console you will need the updated patch below.

	Ingo

---------------------->
Subject: no: tty bkl
From: Ingo Molnar <mingo@...e.hu>
Date: Wed May 07 08:21:22 CEST 2008

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 drivers/char/tty_io.c        |    5 +++--
 drivers/serial/serial_core.c |    2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

Index: linux/drivers/char/tty_io.c
===================================================================
--- linux.orig/drivers/char/tty_io.c
+++ linux/drivers/char/tty_io.c
@@ -2844,9 +2844,10 @@ out:
 
 static int tty_release(struct inode *inode, struct file *filp)
 {
-	lock_kernel();
+	/* DANGEROUS - can crash your kernel! */
+//	lock_kernel();
 	release_dev(filp);
-	unlock_kernel();
+//	unlock_kernel();
 	return 0;
 }
 
Index: linux/drivers/serial/serial_core.c
===================================================================
--- linux.orig/drivers/serial/serial_core.c
+++ linux/drivers/serial/serial_core.c
@@ -1241,7 +1241,7 @@ static void uart_close(struct tty_struct
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port;
 
-	BUG_ON(!kernel_locked());
+//	BUG_ON(!kernel_locked());
 
 	if (!state || !state->port)
 		return;

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