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Date: Sun, 17 Jan 2010 23:36:34 +0100
From: Andreas Mohr <andi@...as.de>
To: linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
Clemens Ladisch <clemens@...isch.de>,
Ingo Molnar <mingo@...hat.com>
Subject: Really weird timer behaviour (event lag) when emacs21-x is running
(2.6.33-rc4)
Hello all,
I've got a load test which I'm running from time to time,
and today I noticed the following:
everything was quite ok when launching several dozen apps, but as soon
as emacs21-x (Debian) was started, I noticed that top display
actually didn't update any more. Wiggle the mouse / keyboard (as is so
well-known from earlier issues with nohz etc.), and it does update,
immediately.
Well, in fact top display does update even when not wiggling,
just not in 3-second intervals any more, more like every dozen seconds or so.
emacs21-x does lots of
poll([{fd=4, events=POLLIN}], 1, -1) = 1 ([{fd=4, revents=POLLIN}])
read(4,
"\1\0rX\0\0\0\0\35\0\0\1\0\0\0\0\4\0\0\0\0\0\0\0(\35@\n\0\0\0\0", 4096)
= 32
read(4, 0x84a2940, 4096) = -1 EAGAIN (Resource
temporarily unavailable)
--- SIGALRM (Alarm clock) @ 0 (0) ---
gettimeofday({1263766587, 638092}, NULL) = 0
gettimeofday({1263766587, 638236}, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 1000}}, NULL) =
0
sigreturn() = ? (mask now [IO])
poll([{fd=4, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=4,
revents=POLLOUT}])
writev(4, [{"\17\1\2\0z\0\240\3", 8}, {NULL, 0}, {"", 0}], 3) = 8
poll([{fd=4, events=POLLIN}], 1, -1) = ? ERESTART_RESTARTBLOCK (To be
restarted)
--- SIGALRM (Alarm clock) @ 0 (0) ---
gettimeofday({1263766587, 647191}, NULL) = 0
gettimeofday({1263766587, 647347}, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 1000}}, NULL) =
0
sigreturn() = ? (mask now [IO])
poll([{fd=4, events=POLLIN}], 1, -1) = ? ERESTART_RESTARTBLOCK (To be
restarted)
--- SIGALRM (Alarm clock) @ 0 (0) ---
gettimeofday({1263766587, 648973}, NULL) = 0
gettimeofday({1263766587, 649117}, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 1000}}, NULL) =
0
sigreturn() = ? (mask now [IO])
poll([{fd=4, events=POLLIN}], 1, -1) = ? ERESTART_RESTARTBLOCK (To be
restarted)
--- SIGALRM (Alarm clock) @ 0 (0) ---
gettimeofday({1263766587, 650808}, NULL) = 0
gettimeofday({1263766587, 650956}, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 1000}}, NULL) =
0
sigreturn() = ? (mask now [IO])
poll([{fd=4, events=POLLIN}], 1, -1) = ? ERESTART_RESTARTBLOCK (To be
restarted)
--- SIGALRM (Alarm clock) @ 0 (0) ---
gettimeofday({1263766587, 652597}, NULL) = 0
gettimeofday({1263766587, 652741}, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 1000}}, NULL) =
0
sigreturn() = ? (mask now [IO])
poll([{fd=4, events=POLLIN}], 1, -1) = ? ERESTART_RESTARTBLOCK (To be
restarted)
--- SIGALRM (Alarm clock) @ 0 (0) ---
gettimeofday({1263766587, 657317}, NULL) = 0
gettimeofday({1263766587, 657471}, NULL) = 0
setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 1000}}, NULL) =
0
Once emacs21-x window gets shown on screen, I get much higher sys times
than before.
A typical top output is:
top - 23:21:24 up 45 min, 6 users, load average: 1.03, 2.02, 2.22
Tasks: 143 total, 3 running, 140 sleeping, 0 stopped, 0 zombie
Cpu(s): 41.7%us, 58.3%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si,
0.0%st
Mem: 510984k total, 499656k used, 11328k free, 7020k buffers
Swap: 755044k total, 87656k used, 667388k free, 141132k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2409 root 20 0 163m 58m 4940 R 51.9 11.7 5:51.54 Xorg
5496 andi 20 0 15084 8236 3908 S 21.7 1.6 0:11.01 emacs21-x
2949 andi 20 0 14120 4736 3508 S 19.3 0.9 1:44.62 icewm
4062 andi 20 0 30088 2960 1668 S 1.9 0.6 0:13.61 xmms
2953 andi 20 0 136m 15m 8588 S 1.4 3.0 0:43.91
x-terminal-emul
4063 andi 20 0 218m 24m 6652 S 1.1 4.8 0:09.35 xine
With emacs21-x killed:
top - 23:22:58 up 47 min, 6 users, load average: 1.25, 1.85, 2.14
Tasks: 141 total, 1 running, 140 sleeping, 0 stopped, 0 zombie
Cpu(s): 13.6%us, 8.6%sy, 0.0%ni, 77.5%id, 0.3%wa, 0.0%hi, 0.0%si,
0.0%st
Mem: 510984k total, 496572k used, 14412k free, 7096k buffers
Swap: 755044k total, 89032k used, 666012k free, 142860k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2409 root 20 0 163m 58m 5060 S 10.2 11.7 6:31.77 Xorg
2953 andi 20 0 136m 17m 10m S 3.6 3.5 0:45.95
x-terminal-emul
4291 andi 20 0 111m 24m 6928 S 1.6 5.0 0:12.35 acroread
2949 andi 20 0 14120 4812 3520 S 1.3 0.9 1:59.53 icewm
4062 andi 20 0 30088 2944 1664 S 1.3 0.6 0:15.21 xmms
Note that this is on a P3/700 with available_clocksource narrowed down
to acpi_pm only, PIT running and lapic enabled (and no HPET either -
IOW very poor hardware environment).
It could just as well be that the setitimer loop that emacs21-x does is
simply overwhelming the system so much (and with the 50% system load as
indicated above! Perhaps due to PIT I/O penalties or so...)
that it's not even able to update the 3-second refresh of top any more.
However, since wiggling the mouse almost always _immediately_
updates top output, this suggests that the system isn't really _fully_
overloaded, yet we simply somewhere miss the chance to process waiting
events, since we're so busy reprogramming timers or so.
Or, even more drastically speaking, the timer reprogramming/insertion (of a
painfully slow legacy timer device) being done by a different app
actually seems to manage to make us actively lose triggers
of the unrelated running top.
Or it could just be a timer lock contention issue...
Any thoughts?
Andreas Mohr
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