linux-kernel - Re: [PATCH rcu 13/14] workqueue: Make queue_rcu_work() use call_rcu

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Date:   Mon, 24 Oct 2022 18:55:16 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org
Subject: Re: [PATCH rcu 13/14] workqueue: Make queue_rcu_work() use
 call_rcu_flush()

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@...il.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.  ;-)
> 
Right.

urezki@...38:~/data/raid0/coding/linux.git$ git tag --contains
51824b780b719c53113dc39e027fbf670dc66028
v6.1-rc1
v6.1-rc2
urezki@...38:~/data/raid0/coding/linux.git$

--
Uladzislau Rezki