Messages in this thread | | | Date | Thu, 17 Jun 2010 10:56:15 -0400 | From | Brian Bloniarz <> | Subject | Re: Slow pty's (was Re: libdivecomputer interfaces?) |
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On 06/17/2010 09:24 AM, Peter Zijlstra wrote: > On Thu, 2010-06-17 at 12:50 +0200, Mike Galbraith wrote: > >> sched: do not ratelimit NOHZ when the tick is stopped. >> >> Chris Wedgwood reports that 39c0cbe sched: Rate-limit nohz causes a serial >> console regression, unresponsiveness, and indeed it does. The below fixes >> it by not skipping out when the tick has been stopped. >> >> Tested that the throughput benefit of ratelimiting is still intact. It is. >> >> Signed-off-by: Mike Galbraith <efault@gmx.de> >> Reported-by: Chris Wedgwood <cw@f00f.org> > >> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c >> index 5f171f0..83c5129 100644 >> --- a/kernel/time/tick-sched.c >> +++ b/kernel/time/tick-sched.c >> @@ -315,7 +315,7 @@ void tick_nohz_stop_sched_tick(int inidle) >> goto end; >> } >> >> - if (nohz_ratelimit(cpu)) >> + if (!ts->tick_stopped && nohz_ratelimit(cpu)) >> goto end; >> >> ts->idle_calls++; >> > > > Humm,. the code around there suggests something like the below, but I > must admit its been a while since I really read all that nohz stuff, > Thomas, any preferences?
I tested Peter's variant, it eliminates the kvm console echo latency that I was seeing. (I haven't tried Mike's earlier variant).
Tested-by: Brian Bloniarz <bmb@athenacr.com>
> --- > kernel/time/tick-sched.c | 5 +---- > 1 files changed, 1 insertions(+), 4 deletions(-) > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 5f171f0..e0707ea 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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