From: Vincent Guittot <vincent.guittot@linaro.org>
To: Christoph Lameter <cl@linux.com>
Cc: Bharata B Rao <bharata@linux.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
guro@fb.com, vbabka@suse.cz, Shakeel Butt <shakeelb@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
aneesh.kumar@linux.ibm.com
Subject: Re: [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order
Date: Thu, 21 Jan 2021 11:48:33 +0100 [thread overview]
Message-ID: <CAKfTPtDtTkuKRJH-otGM1ZUP1tZUAfLMr5prRiN_T68bZ5m5Bw@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2101210959060.100764@www.lameter.com>
On Thu, 21 Jan 2021 at 11:01, Christoph Lameter <cl@linux.com> wrote:
>
> On Thu, 21 Jan 2021, Bharata B Rao wrote:
>
> > > The problem is that calculate_order() is called a number of times
> > > before secondaries CPUs are booted and it returns 1 instead of 224.
> > > This makes the use of num_online_cpus() irrelevant for those cases
> > >
> > > After adding in my command line "slub_min_objects=36" which equals to
> > > 4 * (fls(num_online_cpus()) + 1) with a correct num_online_cpus == 224
> > > , the regression diseapears:
> > >
> > > 9 iterations of hackbench -l 16000 -g 16: 3.201sec (+/- 0.90%)
> >
> > Should we have switched to num_present_cpus() rather than
> > num_online_cpus()? If so, the below patch should address the
> > above problem.
>
> There is certainly an initcall after secondaries are booted where we could
> redo the calculate_order?
>
> Or the num_online_cpus needs to be up to date earlier. Why does this issue
> not occur on x86? Does x86 have an up to date num_online_cpus earlier?
I have added a printk in calculate_order() :
pr_info(" SLUB calculate_order cmd %d min %d online %d
present %d possible %d cpus %d", slub_min_objects, min_objects,
num_online_cpus(), num_present_cpus(), num_possible_cpus(),
nr_cpu_ids);
And checked with
qemu-system-x86_64 -kernel bzImage -nographic -smp 4 -append "console=ttyS0"
[ 0.064927] SLUB calculate_order cmd 0 min 8 online 1 present 4
possible 4 cpus 4
[ 0.064970] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
The num_online_cpus has the same behavior as on my platform and
num_online_cpus = 1 when kmem_cache_init() is called
Only the num_present_cpus = 4 from the beginning but that's probably
just because it runs in a VM
Also it's interesting to notice that num_possible_cpus and nr_cpu_ids
are set to the correct value
>
>
next prev parent reply other threads:[~2021-01-21 10:48 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-18 8:27 [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order Bharata B Rao
2020-11-18 11:25 ` Vlastimil Babka
2020-11-18 19:34 ` Roman Gushchin
2020-11-18 19:53 ` David Rientjes
2021-01-20 17:36 ` Vincent Guittot
2021-01-21 5:30 ` Bharata B Rao
2021-01-21 9:09 ` Vincent Guittot
2021-01-21 10:01 ` Christoph Lameter
2021-01-21 10:48 ` Vincent Guittot [this message]
2021-01-21 18:19 ` Vlastimil Babka
2021-01-22 8:03 ` Vincent Guittot
2021-01-22 12:03 ` Vlastimil Babka
2021-01-22 13:16 ` Vincent Guittot
2021-01-23 5:16 ` Bharata B Rao
2021-01-23 12:32 ` Vincent Guittot
2021-01-25 11:20 ` Vlastimil Babka
2021-01-26 23:03 ` Will Deacon
2021-01-27 9:10 ` Christoph Lameter
2021-01-27 11:04 ` Vlastimil Babka
2021-02-03 11:10 ` Bharata B Rao
2021-02-04 7:32 ` Vincent Guittot
2021-02-04 9:07 ` Christoph Lameter
2021-02-04 9:33 ` Vlastimil Babka
2021-02-08 13:41 ` [PATCH] mm, slub: better heuristic for number of cpus when calculating slab order Vlastimil Babka
2021-02-08 14:54 ` Vincent Guittot
2021-02-10 14:07 ` Mel Gorman
2021-01-22 13:05 ` [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order Jann Horn
2021-01-22 13:09 ` Jann Horn
2021-01-22 15:27 ` Vlastimil Babka
2021-01-25 4:28 ` Bharata B Rao
2021-01-26 8:52 ` Michal Hocko
2021-01-26 13:38 ` Vincent Guittot
2021-01-26 13:59 ` Michal Hocko
2021-01-28 13:45 ` Mel Gorman
2021-01-28 13:57 ` Michal Hocko
2021-01-28 14:42 ` Mel Gorman
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