increased vmap_area_lock contentions on "n_tty: Move buffers inton_tty_data"
From: Fengguang Wu
Date: Thu Sep 12 2013 - 20:51:46 EST
Hi Peter,
FYI, we noticed much increased vmap_area_lock contentions since this
commit:
commit 20bafb3d23d108bc0a896eb8b7c1501f4f649b77
Author: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Date: Sat Jun 15 10:21:19 2013 -0400
n_tty: Move buffers into n_tty_data
Reduce pointer reloading and improve locality-of-reference;
allocate read_buf and echo_buf within struct n_tty_data.
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
:040000 040000 96d92e4e242c4b2ff11b25c005bccd093865b350 2822d87b2425c3e7adc7b722a20d739c9d4a3046 M drivers
bisect run success
# bad: [9cdfea961eeaf9b6b939fb9dc822a204a1d94d08] Merge remote-tracking branch 'ipvs-next/master' into devel-hourly-2013090112
# good: [d4e4ab86bcba5a72779c43dc1459f71fea3d89c8] Linux 3.11-rc5
git bisect start '9cdfea961eeaf9b6b939fb9dc822a204a1d94d08' 'd4e4ab86bcba5a72779c43dc1459f71fea3d89c8' '--'
# good: [903bc7e8c2a4f9ef8e40aed615ed48023f9460e3] Merge remote-tracking branch 'spi/for-next'
git bisect good 903bc7e8c2a4f9ef8e40aed615ed48023f9460e3
# bad: [d926318427c1fa8df182d3dcd7f802d7d0609225] Merge remote-tracking branch 'bcon/master'
git bisect bad d926318427c1fa8df182d3dcd7f802d7d0609225
# bad: [adcb2bcd0dd2bb88f21180c8ffb9ec2549f4d883] Merge remote-tracking branch 'usb/usb-next'
git bisect bad adcb2bcd0dd2bb88f21180c8ffb9ec2549f4d883
# good: [a83605266423437d8afe73cbd538df33cf8fb32b] Merge remote-tracking branch 'driver-core/driver-core-next'
git bisect good a83605266423437d8afe73cbd538df33cf8fb32b
# good: [224563b6ce034b82f8511969d9496113da34fb2c] Merge tag 'for-usb-next-2013-08-15' of git://git.kernel.org/pub/scm/linux/kernel/git/sarah/xhci into usb-next
git bisect good 224563b6ce034b82f8511969d9496113da34fb2c
# bad: [5284eba7b37dfeffe75bfdf81a13e9efebe0480a] serial/arc-uart: Handle Rx Error Interrupts w/o any data
git bisect bad 5284eba7b37dfeffe75bfdf81a13e9efebe0480a
# bad: [7d88d637a3c75257b7611f9feee0c17fa187ecc9] n_tty: Factor standard per-char i/o into separate fn
git bisect bad 7d88d637a3c75257b7611f9feee0c17fa187ecc9
# good: [11b9faa44df76189b8346ff602a2c01c610c37eb] tty: Merge tty_buffer_find() into tty_buffer_alloc()
git bisect good 11b9faa44df76189b8346ff602a2c01c610c37eb
# good: [019ebdf9f26fd2e43b9e1af576835183e95dc82e] n_tty: Eliminate echo_commit memory barrier
git bisect good 019ebdf9f26fd2e43b9e1af576835183e95dc82e
# bad: [1bb9d562856279a217a4e581a803dee9bb48a708] n_tty: Rename process_char_map to char_map
git bisect bad 1bb9d562856279a217a4e581a803dee9bb48a708
# good: [9dfd16ddea9bdbc8343340e543732db0a467ae32] n_tty: Avoid false-sharing echo buffer indices
git bisect good 9dfd16ddea9bdbc8343340e543732db0a467ae32
# good: [8cb06c983822103da1cfe57b9901e60a00e61f67] n_tty: Remove alias ptrs in __receive_buf()
git bisect good 8cb06c983822103da1cfe57b9901e60a00e61f67
# bad: [20bafb3d23d108bc0a896eb8b7c1501f4f649b77] n_tty: Move buffers into n_tty_data
git bisect bad 20bafb3d23d108bc0a896eb8b7c1501f4f649b77
# first bad commit: [20bafb3d23d108bc0a896eb8b7c1501f4f649b77] n_tty: Move buffers into n_tty_data
Compare of all good/bad commits in this bisect:
lock_stat.vmap_area_lock.contentions
22000 ++-----------------------------------------------------------------+
20000 ++O O O O O O O O OO O O OO O O O OO O O O O O O O O |
O OO OO O O O |
18000 ++ |
16000 ++ |
| |
14000 ++ |
12000 ++ |
10000 ++ |
| |
8000 ++ |
6000 ++ |
| |
4000 *+*.**.*.*.*.**.*.*.*.*.**.*.*.*.**.*.*.*.**.*.*.*.*.**.*.*.*.**.*.*
2000 ++-----------------------------------------------------------------+
lock_stat.vmap_area_lock.contentions.get_vmalloc_info
45000 ++-----------------------------------------------------------------+
| O O O O O O O |
40000 O+ OO O O O OO O O O OO O O OO O O OO O O OO O O O |
35000 ++ |
| |
30000 ++ |
| |
25000 ++ |
| |
20000 ++ |
15000 ++ |
| |
10000 ++ |
| *.*. *. .*. .*. .*.*. |
5000 *+*-**-*-*-*-**-*-*-*-*-*----*-*-*--*---*-**-*-*-*---**-----*-**-*-*
>From 20bafb3d23d108bc0a896eb8b7c1501f4f649b77 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Date: Sat, 15 Jun 2013 10:21:19 -0400
Subject: [PATCH] n_tty: Move buffers into n_tty_data
Reduce pointer reloading and improve locality-of-reference;
allocate read_buf and echo_buf within struct n_tty_data.
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/n_tty.c | 25 +++++++++----------------
1 file changed, 9 insertions(+), 16 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index d6eba99..51cbdd2 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -105,9 +105,9 @@ struct n_tty_data {
unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
/* shared by producer and consumer */
- char *read_buf;
+ char read_buf[N_TTY_BUF_SIZE];
DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
- unsigned char *echo_buf;
+ unsigned char echo_buf[N_TTY_BUF_SIZE];
int minimum_to_wake;
@@ -1695,9 +1695,7 @@ static void n_tty_close(struct tty_struct *tty)
if (tty->link)
n_tty_packet_mode_flush(tty);
- kfree(ldata->read_buf);
- kfree(ldata->echo_buf);
- kfree(ldata);
+ vfree(ldata);
tty->disc_data = NULL;
}
@@ -1715,7 +1713,8 @@ static int n_tty_open(struct tty_struct *tty)
{
struct n_tty_data *ldata;
- ldata = kzalloc(sizeof(*ldata), GFP_KERNEL);
+ /* Currently a malloc failure here can panic */
+ ldata = vmalloc(sizeof(*ldata));
if (!ldata)
goto err;
@@ -1723,16 +1722,14 @@ static int n_tty_open(struct tty_struct *tty)
mutex_init(&ldata->atomic_read_lock);
mutex_init(&ldata->output_lock);
- /* These are ugly. Currently a malloc failure here can panic */
- ldata->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
- ldata->echo_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
- if (!ldata->read_buf || !ldata->echo_buf)
- goto err_free_bufs;
-
tty->disc_data = ldata;
reset_buffer_flags(tty->disc_data);
ldata->column = 0;
+ ldata->canon_column = 0;
ldata->minimum_to_wake = 1;
+ ldata->num_overrun = 0;
+ ldata->no_room = 0;
+ ldata->lnext = 0;
tty->closing = 0;
/* indicate buffer work may resume */
clear_bit(TTY_LDISC_HALTED, &tty->flags);
@@ -1740,10 +1737,6 @@ static int n_tty_open(struct tty_struct *tty)
tty_unthrottle(tty);
return 0;
-err_free_bufs:
- kfree(ldata->read_buf);
- kfree(ldata->echo_buf);
- kfree(ldata);
err:
return -ENOMEM;
}
--
1.8.3.2