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Subjectvcs: hook sysfs devices into object lifetime instead of "binding"
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Date
From: Kay Sievers <kay.sievers@vrfy.org>
Subject: 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>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
---
drivers/char/vc_screen.c | 16 ++++++++--------
drivers/char/vt.c | 5 +++--
include/linux/console.h | 4 ++--
3 files changed, 13 insertions(+), 12 deletions(-)

--- a/drivers/char/vc_screen.c
+++ b/drivers/char/vc_screen.c
@@ -479,18 +479,18 @@ static const struct file_operations vcs_

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)
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -778,6 +778,7 @@ int vc_allocate(unsigned int currcons) /
}
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 *t
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_stru
BUG_ON(vc == NULL);
acquire_console_sem();
vc->vc_tty = NULL;
- vcs_remove_sysfs(tty);
release_console_sem();
tty_shutdown(tty);
}
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -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


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