Re: [PATCH tip/core/rcu 11/23] rcu: Adjust debugfs tracing forkthread-based quiescent-state forcing

From: Josh Triplett
Date: Sun Sep 02 2012 - 02:06:55 EST

On Thu, Aug 30, 2012 at 11:18:26AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>
> Moving quiescent-state forcing into a kthread dispenses with the need
> for the ->n_rp_need_fqs field, so this commit removes it.
>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>

> Documentation/RCU/trace.txt | 43 ++++++++++++++++---------------------------
> kernel/rcutree.h | 1 -
> kernel/rcutree_trace.c | 3 +--
> 3 files changed, 17 insertions(+), 30 deletions(-)
>
> diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
> index f6f15ce..672d190 100644
> --- a/Documentation/RCU/trace.txt
> +++ b/Documentation/RCU/trace.txt
> @@ -333,23 +333,23 @@ o Each element of the form "1/1 0:127 ^0" represents one struct
> The output of "cat rcu/rcu_pending" looks as follows:
>
> rcu_sched:
> - 0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nf=6445 nn=146741
> - 1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nf=5912 nn=155792
> - 2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nf=1201 nn=136629
> - 3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nf=207 nn=137723
> - 4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nf=3529 nn=123110
> - 5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nf=201 nn=137456
> - 6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nf=4202 nn=120834
> - 7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nf=41 nn=144888
> + 0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nn=146741
> + 1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nn=155792
> + 2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nn=136629
> + 3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nn=137723
> + 4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nn=123110
> + 5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nn=137456
> + 6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nn=120834
> + 7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nn=144888
> rcu_bh:
> - 0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nf=2 nn=145314
> - 1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nf=3 nn=143180
> - 2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nf=0 nn=117936
> - 3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nf=0 nn=134863
> - 4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nf=0 nn=110671
> - 5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nf=0 nn=133235
> - 6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nf=2 nn=110921
> - 7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nf=0 nn=118542
> + 0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nn=145314
> + 1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nn=143180
> + 2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nn=117936
> + 3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nn=134863
> + 4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nn=110671
> + 5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nn=133235
> + 6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nn=110921
> + 7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nn=118542
>
> As always, this is once again split into "rcu_sched" and "rcu_bh"
> portions, with CONFIG_TREE_PREEMPT_RCU kernels having an additional
> @@ -377,17 +377,6 @@ o "gpc" is the number of times that an old grace period had
> o "gps" is the number of times that a new grace period had started,
> but this CPU was not yet aware of it.
>
> -o "nf" is the number of times that this CPU suspected that the
> - current grace period had run for too long, and thus needed to
> - be forced.
> -
> - Please note that "forcing" consists of sending resched IPIs
> - to holdout CPUs. If that CPU really still is in an old RCU
> - read-side critical section, then we really do have to wait for it.
> - The assumption behing "forcing" is that the CPU is not still in
> - an old RCU read-side critical section, but has not yet responded
> - for some other reason.
> -
> o "nn" is the number of times that this CPU needed nothing. Alert
> readers will note that the rcu "nn" number for a given CPU very
> closely matches the rcu_bh "np" number for that same CPU. This
> diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> index 1f26b1f..36916df 100644
> --- a/kernel/rcutree.h
> +++ b/kernel/rcutree.h
> @@ -312,7 +312,6 @@ struct rcu_data {
> unsigned long n_rp_cpu_needs_gp;
> unsigned long n_rp_gp_completed;
> unsigned long n_rp_gp_started;
> - unsigned long n_rp_need_fqs;
> unsigned long n_rp_need_nothing;
>
> /* 6) _rcu_barrier() and OOM callbacks. */
> diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
> index abffb48..f54f0ce 100644
> --- a/kernel/rcutree_trace.c
> +++ b/kernel/rcutree_trace.c
> @@ -386,10 +386,9 @@ static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)
> rdp->n_rp_report_qs,
> rdp->n_rp_cb_ready,
> rdp->n_rp_cpu_needs_gp);
> - seq_printf(m, "gpc=%ld gps=%ld nf=%ld nn=%ld\n",
> + seq_printf(m, "gpc=%ld gps=%ld nn=%ld\n",
> rdp->n_rp_gp_completed,
> rdp->n_rp_gp_started,
> - rdp->n_rp_need_fqs,
> rdp->n_rp_need_nothing);
> }
>
> --
> 1.7.8
>
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