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Commit 4995f8ef authored by Kay Sievers's avatar Kay Sievers Committed by Greg Kroah-Hartman
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vcs: hook sysfs devices into object lifetime instead of "binding" 



During bootup performance tracing I noticed many occurrences of
vca* device creation and removal, leading to the usual userspace
uevent processing, which are, in this case, rather pointless.

A simple test showing the kernel timing (not including all the
work userspace has to do), gives us these numbers:
  $ time for i in `seq 1000`; do echo a > /dev/tty2; done
  real    0m1.142s
  user    0m0.015s
  sys     0m0.540s

If we move the hook for the vcs* driver core devices from the
tty "binding" to the vc allocation/deallocation, which is what
the vcs* devices represent, we get the following numbers:
  $ time for i in `seq 1000`; do echo a > /dev/tty2; done
  real    0m0.152s
  user    0m0.030s
  sys     0m0.072s

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarKay Sievers <kay.sievers@vrfy.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent ce21c7bc

drivers/char/vc_screen.c

+8 −8
Original line number Diff line number Diff line
@@ -479,18 +479,18 @@ static const struct file_operations vcs_fops = { 


static struct class *vc_class;



void vcs_make_sysfs(struct tty_struct *tty)

void vcs_make_sysfs(int index)

{

	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, tty->index + 1), NULL,

		      "vcs%u", tty->index + 1);

	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, tty->index + 129), NULL,

		      "vcsa%u", tty->index + 1);

	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,

		      "vcs%u", index + 1);

	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,

		      "vcsa%u", index + 1);

}



void vcs_remove_sysfs(struct tty_struct *tty)

void vcs_remove_sysfs(int index)

{

	device_destroy(vc_class, MKDEV(VCS_MAJOR, tty->index + 1));

	device_destroy(vc_class, MKDEV(VCS_MAJOR, tty->index + 129));

	device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));

	device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));

}



int __init vcs_init(void)

drivers/char/vt.c

+3 −2
Original line number Diff line number Diff line
@@ -778,6 +778,7 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */ 
	    }

	    vc->vc_kmalloced = 1;

	    vc_init(vc, vc->vc_rows, vc->vc_cols, 1);

	    vcs_make_sysfs(currcons);

	    atomic_notifier_call_chain(&vt_notifier_list, VT_ALLOCATE, &param);

	}

	return 0;
@@ -987,7 +988,9 @@ void vc_deallocate(unsigned int currcons) 
	if (vc_cons_allocated(currcons)) {

		struct vc_data *vc = vc_cons[currcons].d;

		struct vt_notifier_param param = { .vc = vc };



		atomic_notifier_call_chain(&vt_notifier_list, VT_DEALLOCATE, &param);

		vcs_remove_sysfs(currcons);

		vc->vc_sw->con_deinit(vc);

		put_pid(vc->vt_pid);

		module_put(vc->vc_sw->owner);
@@ -2775,7 +2778,6 @@ static int con_open(struct tty_struct *tty, struct file *filp) 
				tty->termios->c_iflag |= IUTF8;

			else

				tty->termios->c_iflag &= ~IUTF8;

			vcs_make_sysfs(tty);

			release_console_sem();

			return ret;

		}
@@ -2795,7 +2797,6 @@ static void con_shutdown(struct tty_struct *tty) 
	BUG_ON(vc == NULL);

	acquire_console_sem();

	vc->vc_tty = NULL;

	vcs_remove_sysfs(tty);

	release_console_sem();

	tty_shutdown(tty);

}

include/linux/console.h

+2 −2
Original line number Diff line number Diff line
@@ -137,8 +137,8 @@ extern void resume_console(void); 
int mda_console_init(void);

void prom_con_init(void);



void vcs_make_sysfs(struct tty_struct *tty);

void vcs_remove_sysfs(struct tty_struct *tty);

void vcs_make_sysfs(int index);

void vcs_remove_sysfs(int index);



/* Some debug stub to catch some of the obvious races in the VT code */

#if 1