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

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Date:	Wed, 07 May 2008 15:05:00 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
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


On Wed, 2008-05-07 at 08:28 +0200, Ingo Molnar wrote:
> * 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.
I tested it on my 8-core stoakley. The result is 4% worse than the one of pure
2.6.26-rc1. Still not good.

> 
> 	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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