Re: [net] 4890b686f4: netperf.Throughput_Mbps -69.4% regression

Shakeel Butt
2022-07-01T15:47:48Z

On Mon, Jun 27, 2022 at 8:49 PM Feng Tang <feng.tang@intel.com> wrote:
>
> On Mon, Jun 27, 2022 at 06:25:59PM +0200, Eric Dumazet wrote:
> > On Mon, Jun 27, 2022 at 4:48 PM Feng Tang <feng.tang@intel.com> wrote:
> > >
> > > Yes, I also analyzed the perf-profile data, and made some layout changes
> > > which could recover the changes from 69% to 40%.
> > >
> > > 7c80b038d23e1f4c 4890b686f4088c90432149bd6de 332b589c49656a45881bca4ecc0
> > > ---------------- --------------------------- ---------------------------
> > > 15722 -69.5% 4792 -40.8% 9300 netperf.Throughput_Mbps
> > >
> >
> > I simply did the following and got much better results.
> >
> > But I am not sure if updates to ->usage are really needed that often...
> >
> >
> > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
> > index 679591301994d316062f92b275efa2459a8349c9..e267be4ba849760117d9fd041e22c2a44658ab36
> > 100644
> > --- a/include/linux/page_counter.h
> > +++ b/include/linux/page_counter.h
> > @@ -3,12 +3,15 @@
> > #define _LINUX_PAGE_COUNTER_H
> >
> > #include <linux/atomic.h>
> > +#include <linux/cache.h>
> > #include <linux/kernel.h>
> > #include <asm/page.h>
> >
> > struct page_counter {
> > - atomic_long_t usage;
> > - unsigned long min;
> > + /* contended cache line. */
> > + atomic_long_t usage ____cacheline_aligned_in_smp;
> > +
> > + unsigned long min ____cacheline_aligned_in_smp;
> > unsigned long low;
> > unsigned long high;
> > unsigned long max;
> > @@ -27,12 +30,6 @@ struct page_counter {
> > unsigned long watermark;
> > unsigned long failcnt;
> >
> > - /*
> > - * 'parent' is placed here to be far from 'usage' to reduce
> > - * cache false sharing, as 'usage' is written mostly while
> > - * parent is frequently read for cgroup's hierarchical
> > - * counting nature.
> > - */
> > struct page_counter *parent;
> > };
>
> I just tested it, it does perform better (the 4th is with your patch),
> some perf-profile data is also listed.
>
> 7c80b038d23e1f4c 4890b686f4088c90432149bd6de 332b589c49656a45881bca4ecc0 e719635902654380b23ffce908d
> ---------------- --------------------------- --------------------------- ---------------------------
> 15722 -69.5% 4792 -40.8% 9300 -27.9% 11341 netperf.Throughput_Mbps
>
> 0.00 +0.3 0.26 ± 5% +0.5 0.51 +1.3 1.27 ± 2%pp.self.__sk_mem_raise_allocated
> 0.00 +0.3 0.32 ± 15% +1.7 1.74 ± 2% +0.4 0.40 ± 2% pp.self.propagate_protected_usage
> 0.00 +0.8 0.82 ± 7% +0.9 0.90 +0.8 0.84 pp.self.__mod_memcg_state
> 0.00 +1.2 1.24 ± 4% +1.0 1.01 +1.4 1.44 pp.self.try_charge_memcg
> 0.00 +2.1 2.06 +2.1 2.13 +2.1 2.11 pp.self.page_counter_uncharge
> 0.00 +2.1 2.14 ± 4% +2.7 2.71 +2.6 2.60 ± 2% pp.self.page_counter_try_charge
> 1.12 ± 4% +3.1 4.24 +1.1 2.22 +1.4 2.51 pp.self.native_queued_spin_lock_slowpath
> 0.28 ± 9% +3.8 4.06 ± 4% +0.2 0.48 +0.4 0.68 pp.self.sctp_eat_data
> 0.00 +8.2 8.23 +0.8 0.83 +1.3 1.26 pp.self.__sk_mem_reduce_allocated
>
> And the size of 'mem_cgroup' is increased from 4224 Bytes to 4608.

Hi Feng, can you please try two more configurations? Take Eric's patch
of adding ____cacheline_aligned_in_smp in page_counter and for first
increase MEMCG_CHARGE_BATCH to 64 and for second increase it to 128.
Basically batch increases combined with Eric's patch.