From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Uladzislau Rezki <urezki@gmail.com>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, rostedt@goodmis.org
Subject: Re: [PATCH rcu 13/14] workqueue: Make queue_rcu_work() use call_rcu_flush()
Date: Fri, 28 Oct 2022 21:42:30 +0000 [thread overview]
Message-ID: <Y1xMxlT5B7PcAUMP@google.com> (raw)
In-Reply-To: <Y1xIY77sFTyxgAsU@google.com>
On Fri, Oct 28, 2022 at 09:23:47PM +0000, Joel Fernandes wrote:
> On Mon, Oct 24, 2022 at 09:48:19AM -0700, Paul E. McKenney wrote:
> > On Mon, Oct 24, 2022 at 06:25:30PM +0200, Uladzislau Rezki wrote:
> > > >
> > > > You guys might need to agree on the definition of "good" here. Or maybe
> > > > understand the differences in your respective platforms' definitions of
> > > > "good". ;-)
> > > >
> > > Indeed. Bad is when once per-millisecond infinitely :) At least in such use
> > > workload a can detect a power delta and power gain. Anyway, below is a new
> > > trace where i do not use "flush" variant for the kvfree_rcu():
> > >
> > > <snip>
> > > 1. Home screen swipe:
> > > rcuop/0-15 [003] d..1 1792.767750: rcu_batch_start: rcu_preempt CBs=1003 bl=10
> > > rcuop/2-33 [002] d..1 1792.771717: rcu_batch_start: rcu_preempt CBs=934 bl=10
> > > rcuop/3-40 [001] d..1 1794.811816: rcu_batch_start: rcu_preempt CBs=1508 bl=11
> > > rcuop/1-26 [003] d..1 1797.116382: rcu_batch_start: rcu_preempt CBs=2127 bl=16
> > > rcuop/4-48 [001] d..1 1797.124422: rcu_batch_start: rcu_preempt CBs=95 bl=10
> > > rcuop/5-55 [002] d..1 1797.124731: rcu_batch_start: rcu_preempt CBs=143 bl=10
> > > rcuop/6-62 [005] d..1 1798.911719: rcu_batch_start: rcu_preempt CBs=132 bl=10
> > > rcuop/2-33 [002] d..1 1803.003966: rcu_batch_start: rcu_preempt CBs=3797 bl=29
> > > rcuop/0-15 [003] d..1 1803.004707: rcu_batch_start: rcu_preempt CBs=2969 bl=23
> > > 2. App launches:
> > > rcuop/4-48 [005] d..1 1831.087612: rcu_batch_start: rcu_preempt CBs=6141 bl=47
> > > rcuop/7-69 [007] d..1 1831.095578: rcu_batch_start: rcu_preempt CBs=5464 bl=42
> > > rcuop/5-55 [004] d..1 1832.703571: rcu_batch_start: rcu_preempt CBs=8461 bl=66
> > > rcuop/0-15 [004] d..1 1833.731603: rcu_batch_start: rcu_preempt CBs=2548 bl=19
> > > rcuop/1-26 [006] d..1 1833.743691: rcu_batch_start: rcu_preempt CBs=2567 bl=20
> > > rcuop/2-33 [006] d..1 1833.744005: rcu_batch_start: rcu_preempt CBs=2359 bl=18
> > > rcuop/3-40 [006] d..1 1833.744286: rcu_batch_start: rcu_preempt CBs=3681 bl=28
> > > rcuop/4-48 [002] d..1 1838.079777: rcu_batch_start: rcu_preempt CBs=10444 bl=81
> > > rcuop/7-69 [001] d..1 1838.080375: rcu_batch_start: rcu_preempt CBs=12572 bl=98
> > > <...>-62 [002] d..1 1838.080646: rcu_batch_start: rcu_preempt CBs=14135 bl=110
> > > rcuop/6-62 [000] d..1 1838.087722: rcu_batch_start: rcu_preempt CBs=10839 bl=84
> > > <...>-62 [003] d..1 1839.227022: rcu_batch_start: rcu_preempt CBs=1834 bl=14
> > > <...>-26 [001] d..1 1839.963315: rcu_batch_start: rcu_preempt CBs=5769 bl=45
> > > rcuop/2-33 [001] d..1 1839.966485: rcu_batch_start: rcu_preempt CBs=3789 bl=29
> > > <...>-40 [001] d..1 1839.966596: rcu_batch_start: rcu_preempt CBs=6425 bl=50
> > > rcuop/2-33 [005] d..1 1840.541272: rcu_batch_start: rcu_preempt CBs=825 bl=10
> > > rcuop/2-33 [005] d..1 1840.547724: rcu_batch_start: rcu_preempt CBs=44 bl=10
> > > rcuop/2-33 [005] d..1 1841.075759: rcu_batch_start: rcu_preempt CBs=516 bl=10
> > > rcuop/0-15 [002] d..1 1841.695716: rcu_batch_start: rcu_preempt CBs=6312 bl=49
> > > rcuop/0-15 [003] d..1 1841.709714: rcu_batch_start: rcu_preempt CBs=39 bl=10
> > > rcuop/5-55 [004] d..1 1843.112442: rcu_batch_start: rcu_preempt CBs=16007 bl=125
> > > rcuop/5-55 [004] d..1 1843.115444: rcu_batch_start: rcu_preempt CBs=7901 bl=61
> > > rcuop/6-62 [001] dn.1 1843.123983: rcu_batch_start: rcu_preempt CBs=8427 bl=65
> > > rcuop/6-62 [006] d..1 1843.412383: rcu_batch_start: rcu_preempt CBs=981 bl=10
> > > rcuop/0-15 [003] d..1 1844.659812: rcu_batch_start: rcu_preempt CBs=1851 bl=14
> > > rcuop/0-15 [003] d..1 1844.667790: rcu_batch_start: rcu_preempt CBs=135 bl=10
> > > <snip>
> > >
> > > it is much more better. But. As i wrote earlier there is a patch that i have submitted
> > > some time ago improving kvfree_rcu() batching:
> > >
> > > <snip>
> > > commit 51824b780b719c53113dc39e027fbf670dc66028
> > > Author: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > Date: Thu Jun 30 18:33:35 2022 +0200
> > >
> > > rcu/kvfree: Update KFREE_DRAIN_JIFFIES interval
> > >
> > > Currently the monitor work is scheduled with a fixed interval of HZ/20,
> > > which is roughly 50 milliseconds. The drawback of this approach is
> > > low utilization of the 512 page slots in scenarios with infrequence
> > > kvfree_rcu() calls. For example on an Android system:
> > > <snip>
> > >
> > > The trace that i posted was taken without it.
> >
> > And if I am not getting too confused, that patch is now in mainline.
> > So it does make sense to rely on it, then. ;-)
>
> Vlad's patch to change the KFREE_DRAIN_JIFFIES to 5 seconds seems reasonable
> to me. However, can we unify KFREE_DRAIN_JIFFIES and LAZY_FLUSH_JIFFIES ?
>
> One at 5 and other at 10 seems odd, especially because the former seems to
> negate the effects of the latter and anyone tweaking that in the future (say
> via new command line options) should probably tweak them together to increase
> batching.
>
> Testing shows significantly better batching with Vlad's updates, however I am
> wondering why the rcu_callback fires in pairs like that from separate
> kworkers:
>
> kworker/6:1-157 [006] d..1 288.861610: rcu_callback: rcu_preempt rhp=0000000079b895f9 func=rcu_work_rcufn 1214
> kworker/4:2-158 [004] d..1 288.861612: rcu_callback: rcu_preempt rhp=00000000d83fcc90 func=rcu_work_rcufn 798
I think this is just 2 kvfree_call_rcu() happening on 2 different CPUs, and
then the draining happened on 2 different kworkers, so appears normal.
Here is also some more evidence from the user side, of kvfree_call_rcu()
noisiness on ChromeOS. So we definitely need the batching to happen on
ChromeOS:
kworker/u24:6-1448 [005] 77.290344: function: kvfree_call_rcu <-- cfg80211_update_known_bss
ThreadPoolForeg-5130 [011] 77.301101: function: kvfree_call_rcu <-- cgroup_migrate_finish
irq/144-iwlwifi-1010 [004] 77.314367: function: kvfree_call_rcu <-- cfg80211_update_known_bss
ThreadPoolSingl-2050 [004] 77.330359: function: kvfree_call_rcu <-- cgroup_migrate_finish
ThreadPoolSingl-2050 [004] 77.330362: function: kvfree_call_rcu <-- cgroup_migrate_finish
ThreadPoolForeg-5130 [011] 77.331513: function: kvfree_call_rcu <-- cgroup_migrate_finish
patchpaneld-2195 [009] 77.337726: function: kvfree_call_rcu <-- neigh_flush_dev
patchpaneld-2195 [009] 77.337737: function: kvfree_call_rcu <-- __hw_addr_del_entry
patchpaneld-2195 [009] 77.337744: function: kvfree_call_rcu <-- addrconf_ifdown
patchpaneld-2195 [009] 77.337744: function: kvfree_call_rcu <-- __hw_addr_del_entry
irq/144-iwlwifi-1010 [004] 77.633595: function: kvfree_call_rcu <-- cfg80211_update_known_bss
irq/144-iwlwifi-1010 [004] 77.633609: function: kvfree_call_rcu <-- cfg80211_update_known_bss
irq/144-iwlwifi-1010 [004] 77.769844: function: kvfree_call_rcu <-- cfg80211_update_known_bss
kworker/u24:1-9 [008] 77.769858: function: kvfree_call_rcu <-- cfg80211_update_known_bss
irq/144-iwlwifi-1010 [004] 77.880114: function: kvfree_call_rcu <-- cfg80211_update_known_bss
kworker/u24:6-1448 [005] 77.880129: function: kvfree_call_rcu <-- cfg80211_update_known_bss
irq/144-iwlwifi-1010 [004] 77.880131: function: kvfree_call_rcu <-- cfg80211_update_known_bss
kworker/u24:6-1448 [005] 77.880133: function: kvfree_call_rcu <-- cfg80211_update_known_bss
virtio_gpu-5882 [010] 78.337302: function: kvfree_call_rcu <-- context_close
virtio_gpu-5882 [010] 78.337303: function: kvfree_call_rcu <-- i915_driver_postclose
virtio_gpu-5882 [010] 78.346058: function: kvfree_call_rcu <-- fence_notify
virtio_gpu-5882 [010] 78.346070: function: kvfree_call_rcu <-- fence_notify
virtio_gpu-5882 [010] 78.346079: function: kvfree_call_rcu <-- fence_notify
virtio_gpu-5882 [010] 78.346086: function: kvfree_call_rcu <-- fence_notify
virtio_gpu-5882 [010] 78.346184: function: kvfree_call_rcu <-- fence_notify
virtio_gpu-5882 [010] 78.346196: function: kvfree_call_rcu <-- fence_notify
thanks,
- Joel
>
> I wonder if the queued kwork is executing twice accidentally, or something.
> This kernel does have the additional trace patch below, fyi.
>
> Another thought I have is, if we can just keep the kvfree_rcu() mapped to
> call_rcu() via a config option say CONFIG_RCU_LAZY_KFREE, or something.
> Because I am personally not much a fan of the kfree_rcu() induced additional
> timer wake ups and kworker queue+wakeup which we don't need per-se, if we are
> already batching with Lazyfied-call_rcu. Too many moving parts which might
> hurt power.
>
> ---8<-----------------------
>
> From: Joel Fernandes <joelaf@google.com>
> Subject: [PATCH] debug: reorder trace_rcu_callback
>
> Signed-off-by: Joel Fernandes <joelaf@google.com>
> ---
> kernel/rcu/tree.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 73feb09fd51b..a7c175e9533a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2978,10 +2978,6 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> }
>
> check_cb_ovld(rdp);
> - if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
> - return; // Enqueued onto ->nocb_bypass, so just leave.
> - // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
> - rcu_segcblist_enqueue(&rdp->cblist, head);
> if (__is_kvfree_rcu_offset((unsigned long)func))
> trace_rcu_kvfree_callback(rcu_state.name, head,
> (unsigned long)func,
> @@ -2990,6 +2986,11 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> trace_rcu_callback(rcu_state.name, head,
> rcu_segcblist_n_cbs(&rdp->cblist));
>
> + if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
> + return; // Enqueued onto ->nocb_bypass, so just leave.
> + // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
> + rcu_segcblist_enqueue(&rdp->cblist, head);
> +
> /* Go handle any RCU core processing required. */
> if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
> unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
> --
> 2.38.1.273.g43a17bfeac-goog
>
next prev parent reply other threads:[~2022-10-28 21:42 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 22:51 [PATCH rcu 0/14] Lazy call_rcu() updates for v6.2 Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 01/14] rcu: Simplify rcu_init_nohz() cpumask handling Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 02/14] rcu: Fix late wakeup when flush of bypass cblist happens Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 03/14] rcu: Fix missing nocb gp wake on rcu_barrier() Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 04/14] rcu: Make call_rcu() lazy to save power Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 05/14] rcu: Refactor code a bit in rcu_nocb_do_flush_bypass() Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 06/14] rcu: Shrinker for lazy rcu Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 07/14] rcuscale: Add laziness and kfree tests Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 08/14] percpu-refcount: Use call_rcu_flush() for atomic switch Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 09/14] rcu/sync: Use call_rcu_flush() instead of call_rcu Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 10/14] rcu/rcuscale: Use call_rcu_flush() for async reader test Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 11/14] rcu/rcutorture: Use call_rcu_flush() where needed Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 12/14] scsi/scsi_error: Use call_rcu_flush() instead of call_rcu() Paul E. McKenney
2022-10-19 22:51 ` [PATCH rcu 13/14] workqueue: Make queue_rcu_work() use call_rcu_flush() Paul E. McKenney
2022-10-24 0:36 ` Joel Fernandes
2022-10-24 3:15 ` Paul E. McKenney
2022-10-24 10:49 ` Uladzislau Rezki
2022-10-24 12:23 ` Uladzislau Rezki
2022-10-24 14:31 ` Joel Fernandes
2022-10-24 15:39 ` Paul E. McKenney
2022-10-24 16:25 ` Uladzislau Rezki
2022-10-24 16:48 ` Paul E. McKenney
2022-10-24 16:55 ` Uladzislau Rezki
2022-10-24 17:08 ` Uladzislau Rezki
2022-10-24 17:20 ` Joel Fernandes
2022-10-24 17:35 ` Paul E. McKenney
2022-10-24 20:12 ` Joel Fernandes
2022-10-24 20:16 ` Joel Fernandes
2022-10-25 10:48 ` Uladzislau Rezki
2022-10-25 15:05 ` Joel Fernandes
2022-10-26 20:35 ` Uladzislau Rezki
2022-10-24 20:19 ` Paul E. McKenney
2022-10-24 20:26 ` Joel Fernandes
2022-10-24 17:40 ` Uladzislau Rezki
2022-10-24 20:08 ` Joel Fernandes
2022-10-25 10:47 ` Uladzislau Rezki
2022-10-28 21:23 ` Joel Fernandes
2022-10-28 21:42 ` Joel Fernandes [this message]
2022-10-31 13:21 ` Uladzislau Rezki
2022-10-31 13:37 ` Joel Fernandes
2022-10-31 18:15 ` Joel Fernandes
2022-11-01 4:49 ` Uladzislau Rezki
2022-10-24 16:54 ` Joel Fernandes
2022-10-19 22:51 ` [PATCH rcu 14/14] rxrpc: Use call_rcu_flush() instead of call_rcu() Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y1xMxlT5B7PcAUMP@google.com \
--to=joel@joelfernandes.org \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=paulmck@kernel.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=urezki@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.