From: Andrew Morton <akpm@osdl.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Unusually long delay in the kernel
Date: Fri, 16 Sep 2005 23:52:59 -0700 [thread overview]
Message-ID: <20050916235259.61b87069.akpm@osdl.org> (raw)
In-Reply-To: <Pine.LNX.4.44L0.0509161236440.4523-100000@iolanthe.rowland.org>
Alan Stern <stern@rowland.harvard.edu> wrote:
>
> This code excerpt is taken from the start of the control thread for the
> usb-storage driver in 2.6.14-rc1:
>
>
> static int usb_stor_control_thread(void * __us)
> {
> struct us_data *us = (struct us_data *)__us;
> struct Scsi_Host *host = us_to_host(us);
>
> printk(KERN_INFO "Before thread start\n");
> lock_kernel();
>
> /*
> * This thread doesn't need any user-level access,
> * so get rid of all our resources.
> */
> daemonize("usb-storage");
> current->flags |= PF_NOFREEZE;
> unlock_kernel();
> printk(KERN_INFO "After thread start\n");
>
>
> The code between the two printk's takes a long time to run. I don't have
> precise numbers, but it feels like more than 1 second.
>
> (1) Can anyone explain why, or indicate how to speed it up?
What's it doing at the time? (kgdb is great for this sort of thing: hit
^C, go for a wander through the thread callchains).
Presumably it's spinning on the bkl. Is this actually an SMP machine? If
so, perhaps some other process is holding the bkl for a long time. Perhaps
a netdevice spending a long time diddling hardware in an ioctl, something
like that.
> (2) Are the {un}lock_kernel calls really needed?
Definitely not.
That code could be converted to the kthread API btw.
next prev parent reply other threads:[~2005-09-17 6:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-16 16:42 Alan Stern
2005-09-16 17:58 ` Fawad Lateef
2005-09-17 6:52 ` Andrew Morton [this message]
2005-09-17 22:15 ` Alan Stern
2005-09-17 23:41 ` Andrew Morton
2005-09-18 15:05 ` Alan Stern
2005-09-18 20:09 ` Andrew Morton
2005-09-19 14:40 ` [Proposed PATCH] Add kthread_stop_sem Alan Stern
2005-09-19 18:06 ` Unusually long delay in the kernel Alan Stern
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