Slow pty's (was Re: libdivecomputer interfaces?)
in [Kernel]
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From: Peter Zijlstra on 17 Jun 2010 09:30 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(a)gmx.de> > Reported-by: Chris Wedgwood <cw(a)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? --- 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 { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Thomas Gleixner on 17 Jun 2010 10:20 On Thu, 17 Jun 2010, 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(a)gmx.de> > > Reported-by: Chris Wedgwood <cw(a)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? The version below is better as it solves the problem and follows the nohz_ratelimit() advise even in the case where it changes after the tick has been stopped. Thanks, tglx > --- > 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 { > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Mike Galbraith on 17 Jun 2010 10:20 On Thu, 2010-06-17 at 15:24 +0200, Peter Zijlstra wrote: > 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? Mine works. Yours fits and works. -+ vs ----+, you win :) > --- > 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 { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Brian Bloniarz on 17 Jun 2010 11:00
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(a)gmx.de> >> Reported-by: Chris Wedgwood <cw(a)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(a)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 { > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |