lkml.org 
[lkml]   [2017]   [Aug]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set
From
Date


On 08/08/2017 11:32 PM, Paul E. McKenney wrote:
> On Tue, Aug 08, 2017 at 10:50:26PM +0530, Neeraj Upadhyay wrote:
>> If rcu_kick_kthreads is set, and gp is in progress, check_cpu_stall()
>> does checks to figure out whether jiffies is past rsp->jiffies_stall,
>> doing ordered accesses to avoid any false positives for new grace
>> period initialization after a sufficiently large idle period. This
>> extra processing can be skipped if rcu_cpu_stall_suppress is set.
> Just to make sure I understand, the concern is that someone might have
> booted with rcupdate.rcu_cpu_stall_suppress=1 (thus suppressing the RCU
> CPU stall debugging warnings implemented later in check_cpu_stall()),
> but later decided to also boot with rcutree.rcu_kick_kthreads=1 (thus
> enabling kicking kthreads which check for RCU's grace-period kthreads
> not being properly awakened)?
>
> My immediate reaction is that if there is not much point in specifying
> both rcutree.rcu_kick_kthreads=1 and rcupdate.rcu_cpu_stall_suppress=1.
> But is there some use case that I am missing?
>
> Thanx, Paul
For boot time configuration, agree, there isn't much point in enabling
both options. In addition to boot time, rcu_cpu_stall_suppress can
be temporarily enabled during some operations like sysrq; but this may
not be a use case worth consideration.
>
>> Fixes: 8c7c4829a81c ("rcu: Awaken grace-period kthread if too long since FQS")
>> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
>> ---
>> kernel/rcu/tree.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index 51d4c3a..91b7552 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -1562,10 +1562,13 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
>> unsigned long js;
>> struct rcu_node *rnp;
>>
>> - if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
>> - !rcu_gp_in_progress(rsp))
>> + if (!rcu_gp_in_progress(rsp))
>> return;
>> rcu_stall_kick_kthreads(rsp);
>> +
>> + if (rcu_cpu_stall_suppress)
>> + return;
>> +
>> j = jiffies;
>>
>> /*
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>> member of the Code Aurora Forum, hosted by The Linux Foundation
>>

--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation

\
 
 \ /
  Last update: 2017-08-08 20:58    [W:0.030 / U:0.764 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site