Messages in this thread | | | Date | Fri, 02 Oct 2009 15:47:14 -0400 | From | Oren Laadan <> | Subject | Re: [PATCH 01/19] freezer: don't get over-anxious while waiting |
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Rafael J. Wysocki wrote: > On Thursday 01 October 2009, Pavel Machek wrote: >>> Freezing isn't exactly the most latency sensitive operation and >>> there's no reason to burn cpu cycles and power waiting for it to >>> complete. msleep(10) instead of yield(). This should improve >>> reliability of emergency hibernation. >> i don't see how it improves reliability, but its probably ok. >> >> Well... for hibernation anyway. I can imagine cgroup users where >> freeze is so fast that this matters. rjw cc-ed. pavel > > Thanks. I'd like to hear from the cgroup freezer people about that. >
[Adding Matt Helsley to the CC list]
To checkpoint or migrate an application, the cgroup to which it belongs must be frozen first.
It's a bit down the road, but if one seeks minimum application downtime during application checkpoint and/or migration, then a (minimum of) 10ms - or multiples of it - may result in a visible/undesired hick-up.
Perhaps avoid it when freezing a cgroup ? or maybe a way for the user to control this behavior per cgroup ?
Oren.
>>> Signed-off-by: Tejun Heo <tj@kernel.org> >>> --- >>> kernel/power/process.c | 13 +++++++++---- >>> 1 files changed, 9 insertions(+), 4 deletions(-) >>> >>> diff --git a/kernel/power/process.c b/kernel/power/process.c >>> index cc2e553..9d26a0a 100644 >>> --- a/kernel/power/process.c >>> +++ b/kernel/power/process.c >>> @@ -41,7 +41,7 @@ static int try_to_freeze_tasks(bool sig_only) >>> do_gettimeofday(&start); >>> >>> end_time = jiffies + TIMEOUT; >>> - do { >>> + while (true) { >>> todo = 0; >>> read_lock(&tasklist_lock); >>> do_each_thread(g, p) { >>> @@ -62,10 +62,15 @@ static int try_to_freeze_tasks(bool sig_only) >>> todo++; >>> } while_each_thread(g, p); >>> read_unlock(&tasklist_lock); >>> - yield(); /* Yield is okay here */ >>> - if (time_after(jiffies, end_time)) >>> + if (!todo || time_after(jiffies, end_time)) >>> break; >>> - } while (todo); >>> + >>> + /* >>> + * We need to retry. There's no reason to be >>> + * over-anxious about it and waste power. >>> + */ > > The comment above looks like it's only meaningful in the context of the patch. > After it's been applied the meaning of the comment won't be so obvious, I'm > afraid. > >>> + msleep(10); >>> + } >>> >>> do_gettimeofday(&end); >>> elapsed_csecs64 = timeval_to_ns(&end) - timeval_to_ns(&start); > > Thanks, > Rafael
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