From: Michal Hocko <mhocko@kernel.org>
To: kemi <kemi.wang@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Johannes Weiner <hannes@cmpxchg.org>,
Christopher Lameter <cl@linux.com>,
YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Nikolay Borisov <nborisov@suse.com>,
Pavel Tatashin <pasha.tatashin@oracle.com>,
David Rientjes <rientjes@google.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Dave <dave.hansen@linux.intel.com>,
Andi Kleen <andi.kleen@intel.com>,
Tim Chen <tim.c.chen@intel.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Ying Huang <ying.huang@intel.com>, Aaron Lu <aaron.lu@intel.com>,
Aubrey Li <aubrey.li@intel.com>, Linux MM <linux-mm@kvack.org>,
Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 3/5] mm: enlarge NUMA counters threshold size
Date: Thu, 21 Dec 2017 09:59:52 +0100 [thread overview]
Message-ID: <20171221085952.GB4831@dhcp22.suse.cz> (raw)
In-Reply-To: <1fb66dfd-b64c-f705-ea27-a9f2e11729a4@intel.com>
On Thu 21-12-17 16:23:23, kemi wrote:
>
>
> On 2017年12月21日 16:17, Michal Hocko wrote:
[...]
> > Can you see any difference with a more generic workload?
> >
>
> I didn't see obvious improvement for will-it-scale.page_fault1
> Two reasons for that:
> 1) too long code path
> 2) server zone lock and lru lock contention (access to buddy system frequently)
OK. So does the patch helps for anything other than a microbenchmark?
> >> Some thinking about that:
> >> a) the overhead due to cache bouncing caused by NUMA counter update in fast path
> >> severely increase with more and more CPUs cores
> >
> > What is an effect on a smaller system with fewer CPUs?
> >
>
> Several CPU cycles can be saved using single thread for that.
>
> >> b) AFAIK, the typical usage scenario (similar at least)for which this optimization can
> >> benefit is 10/40G NIC used in high-speed data center network of cloud service providers.
> >
> > I would expect those would disable the numa accounting altogether.
> >
>
> Yes, but it is still worthy to do some optimization, isn't?
Ohh, I am not opposing optimizations but you should make sure that they
are worth the additional code and special casing. As I've said I am not
convinced special casing numa counters is good. You can play with the
threshold scaling for larger CPU count but let's make sure that the
benefit is really measurable for normal workloads. Special ones will
disable the numa accounting anyway.
Thanks!
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-12-21 8:59 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-19 6:39 [PATCH v2 0/5] mm: NUMA stats code cleanup and enhancement Kemi Wang
2017-12-19 6:39 ` [PATCH v2 1/5] mm: migrate NUMA stats from per-zone to per-node Kemi Wang
2017-12-19 12:28 ` Michal Hocko
2017-12-20 5:32 ` kemi
2017-12-19 6:39 ` [PATCH v2 2/5] mm: Extends local cpu counter vm_diff_nodestat from s8 to s16 Kemi Wang
2017-12-19 12:38 ` Michal Hocko
2017-12-20 3:05 ` kemi
2017-12-19 16:05 ` Christopher Lameter
2017-12-19 16:20 ` Michal Hocko
2017-12-19 17:21 ` Christopher Lameter
2017-12-20 6:45 ` kemi
2017-12-19 6:39 ` [PATCH v2 3/5] mm: enlarge NUMA counters threshold size Kemi Wang
2017-12-19 12:40 ` Michal Hocko
2017-12-20 5:52 ` kemi
2017-12-20 10:12 ` Michal Hocko
2017-12-20 10:21 ` kemi
2017-12-21 8:06 ` kemi
2017-12-21 8:17 ` Michal Hocko
2017-12-21 8:23 ` kemi
2017-12-21 8:59 ` Michal Hocko [this message]
2017-12-21 10:31 ` kemi
2017-12-22 12:31 ` Michal Hocko
2017-12-21 17:10 ` Christopher Lameter
2017-12-22 2:06 ` kemi
2017-12-26 19:05 ` Christopher Lameter
2017-12-19 6:39 ` [PATCH v2 4/5] mm: use node_page_state_snapshot to avoid deviation Kemi Wang
2017-12-19 12:43 ` Michal Hocko
2017-12-20 6:07 ` kemi
2017-12-20 10:06 ` Michal Hocko
2017-12-20 10:24 ` kemi
2017-12-20 15:58 ` Christopher Lameter
2017-12-21 1:39 ` kemi
2017-12-19 6:39 ` [PATCH v2 5/5] mm: Rename zone_statistics() to numa_statistics() Kemi Wang
2017-12-19 12:44 ` Michal Hocko
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