Re: [patch] speed up / fix the new generic semaphore code (fix AIM740% regression with 2.6.26-rc1)

[Linus Torvalds]

On Fri, 9 May 2008, Alan Cox wrote:
> 
> I don't think fixing n_tty is now a big job if someone wants to take a
> swing at it. The driver write/throttle/etc routines below the n_tty ldisc
> layer are now BKL clean so it should just be the internal locking of the
> buffers, window and the like to tackle.

Well, it turns out that Ingo's fixed statistics actually put the real cost 
in fcntl/ioctl/open/release:

    310  down <= lock_kernel <= sys_fcntl <= system_call_after_swapgs <
    332  down <= lock_kernel <= vfs_ioctl <= do_vfs_ioctl <
    380  down <= lock_kernel <= tty_release <= __fput <
    422  down <= lock_kernel <= chrdev_open <= __dentry_open <

rather than the write routines. But it may be that Ingo was just profiling 
two different sections, and it's really all of them.

			Linus
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