[PATCH] Firewire node manager causes up to ~3.25s delay in freezing tasks.

[PATCH] Firewire node manager causes up to ~3.25s delay in freezing tasks.

[Nigel Cunningham]

Hi all.

(Okay, having learnt that ieee1394 != bluetooth, I'll try again :>)

The firewire nodemanager function "nodemgr_host_thread" contains a loop
that calls try_to_freeze near the top of the loop, but then delays for
up to 3.25 seconds (plus time to do work) before getting back to the top
of the loop. When starting a cycle post-boot, this doesn't seem to bite,
but it is causing a noticeable delay at boot time, when freezing
processes prior to starting to read the image.

The following patch adds invocation of try_to_freeze to the subloops
that are used in the body of this function. With these additions, the
time to freeze when starting to resume at boot time is virtually zero.
I'm no expert on bluetooth, and so don't know that we shouldn't check
the return value and jump back to the top of the loop or such like after
being frozen, but I submit it for your consideration.

Signed-off-by: Nigel Cunningham <nigel@tuxonice.net>

 nodemgr.c |    2 ++
 1 file changed, 2 insertions(+)
diff -ruNp 710-nodemanager-freezing.patch-old/drivers/ieee1394/nodemgr.c 710-nodemanager-freezing.patch-new/drivers/ieee1394/nodemgr.c
--- 710-nodemanager-freezing.patch-old/drivers/ieee1394/nodemgr.c	2008-12-06 08:42:08.000000000 +1100
+++ 710-nodemanager-freezing.patch-new/drivers/ieee1394/nodemgr.c	2008-12-09 18:49:26.000000000 +1100
@@ -1685,6 +1685,7 @@ static int nodemgr_host_thread(void *dat
 		g = get_hpsb_generation(host);
 		for (i = 0; i < 4 ; i++) {
 			msleep_interruptible(63);
+			try_to_freeze();
 			if (kthread_should_stop())
 				goto exit;
 
@@ -1725,6 +1726,7 @@ static int nodemgr_host_thread(void *dat
 		/* Sleep 3 seconds */
 		for (i = 3000/200; i; i--) {
 			msleep_interruptible(200);
+			try_to_freeze();
 			if (kthread_should_stop())
 				goto exit;
 

Re: [PATCH] Firewire node manager causes up to ~3.25s delay in freezing tasks.

[Stefan Richter]

Nigel Cunningham wrote:
> Hi all.
> 
> (Okay, having learnt that ieee1394 != bluetooth, I'll try again :>)
> 
> The firewire nodemanager function "nodemgr_host_thread" contains a loop
> that calls try_to_freeze near the top of the loop, but then delays for
> up to 3.25 seconds (plus time to do work) before getting back to the top
> of the loop. When starting a cycle post-boot, this doesn't seem to bite,
> but it is causing a noticeable delay at boot time, when freezing
> processes prior to starting to read the image.

In 2.6.27 and less, these were only 0.25 seconds.  The 3 additional
seconds in 2.6.28-rc are my doing and sort of a regression.  It occurs
to me that I should send this patch to mainline before release.

> The following patch adds invocation of try_to_freeze to the subloops
> that are used in the body of this function. With these additions, the
> time to freeze when starting to resume at boot time is virtually zero.
> I'm no expert on bluetooth, and so don't know that we shouldn't check
> the return value and jump back to the top of the loop or such like after
> being frozen, but I submit it for your consideration.
> 
> Signed-off-by: Nigel Cunningham <nigel@tuxonice.net>

As far as I can tell, try_to_freeze() without any jump is correct.

>  nodemgr.c |    2 ++
>  1 file changed, 2 insertions(+)
> diff -ruNp 710-nodemanager-freezing.patch-old/drivers/ieee1394/nodemgr.c 710-nodemanager-freezing.patch-new/drivers/ieee1394/nodemgr.c
> --- 710-nodemanager-freezing.patch-old/drivers/ieee1394/nodemgr.c	2008-12-06 08:42:08.000000000 +1100
> +++ 710-nodemanager-freezing.patch-new/drivers/ieee1394/nodemgr.c	2008-12-09 18:49:26.000000000 +1100
> @@ -1685,6 +1685,7 @@ static int nodemgr_host_thread(void *dat
>  		g = get_hpsb_generation(host);
>  		for (i = 0; i < 4 ; i++) {
>  			msleep_interruptible(63);
> +			try_to_freeze();
>  			if (kthread_should_stop())
>  				goto exit;
>  

Here we have the goal to proceed only >= 0.25s after the last bus reset
happened.  While the new try_to_freeze() held up nodemgr, another bus
reset may happen.  But we check for this later in the loop and handle
it, so this is OK.

> @@ -1725,6 +1726,7 @@ static int nodemgr_host_thread(void *dat
>  		/* Sleep 3 seconds */
>  		for (i = 3000/200; i; i--) {
>  			msleep_interruptible(200);
> +			try_to_freeze();
>  			if (kthread_should_stop())
>  				goto exit;
>  

Ditto, the rest of the loop catches the case that another bus reset
occurred during the sleep or freeze.

Thanks for what appears to be a regression fix,
-- 
Stefan Richter
-=====-==--- ==-- -=--=
http://arcgraph.de/sr/