> On Oct 31, 2022, at 9:21 AM, Uladzislau Rezki <urezki@xxxxxxxxx> wrote: > > 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 Please let us try to trim emails. That goes for me too. >>>> <...>-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@xxxxxxxxx> >>>> 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 ? >> > This is very good. > > Below is a plot that i have taken during one use-case. It is about three > apps usage in parallel. It was done by running "monkey" test: > > wget ftp://vps418301.ovh.net/incoming/monkey_3_apps_slab_usage_5_minutes.png > > i set up three apps as usage scenario: Google Chrome, YoTube and Camera. > I logged the Slab metric from the /proc/meminfo. Sampling rate is 0.1 second. > > Please have a look at results. It reflects what i am saying. non-flush > kvfree RCU variant makes a memory usage higher. What is not acceptable > for our mobile devices and workloads. Thanks I’ll take a closer look at the data (currently commuting) but here’s a quick reply: I am curious that with the 5 second timer, you are delaying RCU anyway. Are you saying that, adding another 10 on top (due to lazyfying) seems to be causing issues? I find it hard to believe that you cannot give the shrinker enough work within 5 seconds, such that it also triggers the issues you’re seeing. However the workload and data speaks. >> 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. >> > Well. Convert 5 seconds to 10? What will it solve for you? We can do it > and from a kvfree_rcu() perspective nothing really is changed. True. In fact with my last patch, I see almost never even the need to go to RCU. However my point with unification is just to keep it simple for user for 2 knobs that do the same thing. Granted this is a compiler knob but that might change in the future. We already have enough knobs in RCU and as you guys know, I’m a fan of not letting the user mess things up too much. >> 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 wonder if the queued kwork is executing twice accidentally, or something. >> > Because a kfree_rcu_cpu() is a per-cpu thing. Right, got it. >> 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. >> > I am not sure you need it, really. If you wake-up "rcuop" or whatever > with 0.5 second interval or with 5 seconds interval you will not notice > anything in terms of power between both. Yes, you are right. This is not needed considering the improvements you recently made. Cheers, - Joel > > -- > Uladzislau Rezki
