* [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bit better
@ 2009-02-11 21:27 akpm
2009-02-12 9:17 ` Ricard Wanderlof
0 siblings, 1 reply; 4+ messages in thread
From: akpm @ 2009-02-11 21:27 UTC (permalink / raw)
To: dwmw2; +Cc: dilinger, akpm, linux-mtd, dilinger
From: Andres Salomon <dilinger@queued.net>
I've noticed some pretty poor behavior on OLPC machines after bootup, when
gdm/X are starting. The GCD monopolizes the scheduler (which in turns
means it gets to do more nand i/o), which results in processes taking much
much longer than they should to start.
As an example, on an OLPC machine going from OFW to a usable X (via
auto-login gdm) takes 2m 30s. The majority of this time is consumed by
the switch into graphical mode. With this patch, we cut a full 60s off of
bootup time. After bootup, things are much snappier as well.
Note that we have seen a CRC node error with this patch that causes the machine
to fail to boot, but we've also seen that problem without this patch.
Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
fs/jffs2/background.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff -puN fs/jffs2/background.c~jffs2-force-the-jffs2-gc-daemon-to-behave-a-bit-better fs/jffs2/background.c
--- a/fs/jffs2/background.c~jffs2-force-the-jffs2-gc-daemon-to-behave-a-bit-better
+++ a/fs/jffs2/background.c
@@ -95,13 +95,17 @@ static int jffs2_garbage_collect_thread(
spin_unlock(&c->erase_completion_lock);
- /* This thread is purely an optimisation. But if it runs when
- other things could be running, it actually makes things a
- lot worse. Use yield() and put it at the back of the runqueue
- every time. Especially during boot, pulling an inode in
- with read_inode() is much preferable to having the GC thread
- get there first. */
- yield();
+ /* Problem - immediately after bootup, the GCD spends a lot
+ * of time in places like jffs2_kill_fragtree(); so much so
+ * that userspace processes (like gdm and X) are starved
+ * despite plenty of cond_resched()s and renicing. Yield()
+ * doesn't help, either (presumably because userspace and GCD
+ * are generally competing for a higher latency resource -
+ * disk).
+ * This forces the GCD to slow the hell down. Pulling an
+ * inode in with read_inode() is much preferable to having
+ * the GC thread get there first. */
+ schedule_timeout_interruptible(msecs_to_jiffies(50));
/* Put_super will send a SIGKILL and then wait on the sem.
*/
_
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bit better
2009-02-11 21:27 [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bit better akpm
@ 2009-02-12 9:17 ` Ricard Wanderlof
2009-03-16 23:28 ` Aras Vaichas
0 siblings, 1 reply; 4+ messages in thread
From: Ricard Wanderlof @ 2009-02-12 9:17 UTC (permalink / raw)
To: akpm; +Cc: dilinger, dwmw2, linux-mtd, dilinger
On Wed, 11 Feb 2009, akpm@linux-foundation.org wrote:
> I've noticed some pretty poor behavior on OLPC machines after bootup, when
> gdm/X are starting. The GCD monopolizes the scheduler (which in turns
> means it gets to do more nand i/o), which results in processes taking much
> much longer than they should to start.
Can't really comment on how well the patch works, but we've also noticed a
similar slowdown on our systems during startup, so the idea as such is
welcome at any rate.
/Ricard
--
Ricard Wolf Wanderlöf ricardw(at)axis.com
Axis Communications AB, Lund, Sweden www.axis.com
Phone +46 46 272 2016 Fax +46 46 13 61 30
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bit better
2009-02-12 9:17 ` Ricard Wanderlof
@ 2009-03-16 23:28 ` Aras Vaichas
2009-03-17 1:23 ` [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bitbetter Reuben Dowle
0 siblings, 1 reply; 4+ messages in thread
From: Aras Vaichas @ 2009-03-16 23:28 UTC (permalink / raw)
To: Ricard Wanderlof; +Cc: dwmw2, akpm, dilinger, linux-mtd, dilinger
Ricard Wanderlof wrote:
> On Wed, 11 Feb 2009, akpm@linux-foundation.org wrote:
>
>
>> I've noticed some pretty poor behavior on OLPC machines after bootup, when
>> gdm/X are starting. The GCD monopolizes the scheduler (which in turns
>> means it gets to do more nand i/o), which results in processes taking much
>> much longer than they should to start.
>>
>
> Can't really comment on how well the patch works, but we've also noticed a
> similar slowdown on our systems during startup, so the idea as such is
> welcome at any rate.
>
I just posted a message to linux-arm-kernel regarding a similar problem
I have an at91rm9200 based machine with NAND and JFFS2.
I suspected that garbage collection was causing delays of up to 3+
seconds during which time my watchdog patting daemon was not being
scheduled ...
This was causing the watchdog timer to reset my machine but *only* when
it was under significant NAND load i.e. boot time, loading up the main
application while GCD was running.
My solution was to double the watchdog timeout.
Aras
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^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bitbetter
2009-03-16 23:28 ` Aras Vaichas
@ 2009-03-17 1:23 ` Reuben Dowle
0 siblings, 0 replies; 4+ messages in thread
From: Reuben Dowle @ 2009-03-17 1:23 UTC (permalink / raw)
To: Aras Vaichas, Ricard Wanderlof; +Cc: dilinger, akpm, dwmw2, linux-mtd, dilinger
I have also noticed the performance degredation caused by the jffs2
garbage collection. The solution we used to this problem on our product
was to do 'pkill -STOP jffs2_gcd' very early in the boot process, then
right at the end of my boot script put 'sleep 90 && pkill -CONT
jffs2_gcd &'
This sped the boot time up a lot.
Reuben
-----Original Message-----
From: linux-mtd-bounces@lists.infradead.org
[mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of Aras Vaichas
Sent: Tuesday, 17 March 2009 12:29 p.m.
To: Ricard Wanderlof
Cc: dwmw2@infradead.org; akpm@linux-foundation.org; dilinger@debian.org;
linux-mtd@lists.infradead.org; dilinger@queued.net
Subject: Re: [patch 4/9] jffs2: force the jffs2 GC daemon to behave a
bitbetter
Ricard Wanderlof wrote:
> On Wed, 11 Feb 2009, akpm@linux-foundation.org wrote:
>
>
>> I've noticed some pretty poor behavior on OLPC machines after bootup,
>> when gdm/X are starting. The GCD monopolizes the scheduler (which in
>> turns means it gets to do more nand i/o), which results in processes
>> taking much much longer than they should to start.
>>
>
> Can't really comment on how well the patch works, but we've also
> noticed a similar slowdown on our systems during startup, so the idea
> as such is welcome at any rate.
>
I just posted a message to linux-arm-kernel regarding a similar problem
I have an at91rm9200 based machine with NAND and JFFS2.
I suspected that garbage collection was causing delays of up to 3+
seconds during which time my watchdog patting daemon was not being
scheduled ...
This was causing the watchdog timer to reset my machine but *only* when
it was under significant NAND load i.e. boot time, loading up the main
application while GCD was running.
My solution was to double the watchdog timeout.
Aras
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please visit http://www.messagelabs.com/email
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end of thread, other threads:[~2009-03-17 1:23 UTC | newest]
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2009-02-11 21:27 [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bit better akpm
2009-02-12 9:17 ` Ricard Wanderlof
2009-03-16 23:28 ` Aras Vaichas
2009-03-17 1:23 ` [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bitbetter Reuben Dowle
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