On Thu, 2010-07-01 at 16:55 -0500, Timur Tabi wrote:
> On Tue, Jun 29, 2010 at 2:54 PM, Timur Tabi <ti...@freescale.com> wrote:
> > I'm adding support for a new e500-based board (the P1022DS), and in
> > the process I've discovered that enabling CONFIG_NO_HZ (Tickless
> > System / Dynamic Ticks) causes significant responsiveness problems on
> > the serial console. When I type on the console, I see delays of up to
> > a half-second for almost every character. It acts as if there's a
> > background process eating all the CPU.
>
> I finally finished my git-bisect, and it wasn't that helpful. I had
> to skip several commits because the kernel just wouldn't boot:
>
> There are only 'skip'ped commits left to test.
> The first bad commit could be any of:
> 6bc6cf2b61336ed0c55a615eb4c0c8ed5daf3f08
> 8b911acdf08477c059d1c36c21113ab1696c612b
> 21406928afe43f1db6acab4931bb8c886f4d04ce
> 5ca9880c6f4ba4c84b517bc2fed5366adf63d191
> a64692a3afd85fe048551ab89142fd5ca99a0dbd
> f2e74eeac03ffb779d64b66a643c5e598145a28b
> c6ee36c423c3ed1fb86bb3eabba9fc256a300d16
> e12f31d3e5d36328c7fbd0fce40a95e70b59152c
> 13814d42e45dfbe845a0bbe5184565d9236896ae
> b42e0c41a422a212ddea0666d5a3a0e3c35206db
> 39c0cbe2150cbd848a25ba6cdb271d1ad46818ad <== the crime scene
> beac4c7e4a1cc6d57801f690e5e82fa2c9c245c8
> 41acab8851a0408c1d5ad6c21a07456f88b54d40
> 6427462bfa50f50dc6c088c07037264fcc73eca1
> c9494727cf293ae2ec66af57547a3e79c724fec2
> We cannot bisect more!
>
> These correspond to a batch of scheduler patches, most from Mike Galbraith.
>
> I don't know what to do now. I can't test any of these commits. Even
> if I could, they look like they're all part of one set, so I doubt I
> could narrow it down to one commit anyway.
Hi Timur,
This has already fixed. Below is the final fix from tip.
commit 3310d4d38fbc514e7b18bd3b1eea8effdd63b5aa
Author: Peter Zijlstra <pet...@infradead.org>
Date: Thu Jun 17 18:02:37 2010 +0200
nohz: Fix nohz ratelimit
Chris Wedgwood reports that 39c0cbe (sched: Rate-limit nohz) causes a
serial console regression, unresponsiveness, and indeed it does. The
reason is that the nohz code is skipped even when the tick was already
stopped before the nohz_ratelimit(cpu) condition changed.
Move the nohz_ratelimit() check to the other conditions which prevent
long idle sleeps.
Reported-by: Chris Wedgwood <c...@f00f.org>
Tested-by: Brian Bloniarz <b...@athenacr.com>
Signed-off-by: Mike Galbraith <efa...@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Jiri Kosina <jkos...@suse.cz>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Greg KH <gre...@suse.de>
Cc: Alan Cox <a...@lxorguk.ukuu.org.uk>
Cc: OGAWA Hirofumi <hirof...@mail.parknet.co.jp>
Cc: Jef Driesen <jefdrie...@telenet.be>
LKML-Reference: <1276790557.27822.516.ca...@twins>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1d7b9bc..783fbad 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -315,9 +315,6 @@ void tick_nohz_stop_sched_tick(int inidle)
goto end;
}
- if (nohz_ratelimit(cpu))
- goto end;
-
ts->idle_calls++;
/* Read jiffies and the time when jiffies were updated last */
do {
@@ -328,7 +325,7 @@ void tick_nohz_stop_sched_tick(int inidle)
} while (read_seqretry(&xtime_lock, seq));
if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
- arch_needs_cpu(cpu)) {
+ arch_needs_cpu(cpu) || nohz_ratelimit(cpu)) {
next_jiffies = last_jiffies + 1;
delta_jiffies = 1;
} else {
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