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SubjectRe: Slow pty's (was Re: libdivecomputer interfaces?)
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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