From: Marcelo Tosatti <mtosatti@redhat.com>
To: Christoph Lameter <cl@linux.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Rik van Riel <riel@redhat.com>,
Linux RT Users <linux-rt-users@vger.kernel.org>,
cmetcalf@mellanox.com
Subject: Re: [patch 2/2] MM: allow per-cpu vmstat_threshold and vmstat_worker configuration
Date: Fri, 12 May 2017 12:40:28 -0300 [thread overview]
Message-ID: <20170512154026.GA3556@amt.cnet> (raw)
In-Reply-To: <alpine.DEB.2.20.1705121002310.22243@east.gentwo.org>
On Fri, May 12, 2017 at 10:11:14AM -0500, Christoph Lameter wrote:
> On Fri, 12 May 2017, Marcelo Tosatti wrote:
>
> > > A bit confused by this one. The vmstat worker is already disabled if there
> > > are no updates. Also the patches by Chris Metcalf on data plane mode add a
> > > prctl to quiet the vmstat workers.
> > >
> > > Why do we need more than this?
> >
> > If there are vmstat statistic updates on a given CPU, and you don't
> > want intervention from the vmstat worker, you change the behaviour of
> > stat data collection to directly write to the global structures (which
> > disables the performance optimization of collecting data in per-cpu
> > counters).
>
> Hmmm.... Ok. That is going to be expensive if you do this for each
> individual vmstat update.
In our case, vmstat updates are very rare (CPU is dominated by DPDK).
> > This way you can disable vmstat worker (because it causes undesired
> > latencies), while allowing vmstatistics to function properly.
>
> Best then to run the vmstat update mechanism when you leave kernel mode to
> get all the updates in one go.
Again, vmstat updates are very rare (CPU is dominated by DPDK).
> > The prctl from Chris Metcalf patchset allows one to disable vmstat
> > worker per CPU? If so, they replace the functionality of the patch
> > "[patch 3/3] MM: allow per-cpu vmstat_worker configuration"
> > of the -v2 series of my patchset, and we can use it instead.
> >
> > Is it integrated already?
>
> The data plane mode patches disables vmstat processing by updating the
> vmstats immediately if necessary and switching off the kworker thread.
OK this is what my patch set is doing.
> So the kworker wont be running until the next time statistics are checked
> by the shepherd task from a remote cpu.
We don't want kworker thread to ever run.
> If the counters have been updated
> then the shepherd task will reenable the kworker. This is already merged
> and has been working for a long time. Data plan mode has not been merged
> yet but the infrastructure in vmstat.c is there because NOHZ needs it too.
OK.
>
> See linux/vmstat.c:quiet_vmstat()
>
> It would be easy to add a /proc file that allows the quieting of the
> vmstat workers for a certain cpu. Just make it call the quiet_vmstat() on
> the right cpu.
>
> This will quiet vmstat down. The shepherd task will check the stats in 2
> second intervals and will then reenable when necessasry.
>
> Note that we already are updating the global structures directly if the
> differential gets too high. Reducing the differential may get you what you
> want.
Yes, we reduce the differential to 1 (== direct updates to global
structures).
OK, i'll check if the patches from Chris work for us and then add
Tested-by on that.
Thanks.
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next prev parent reply other threads:[~2017-05-12 15:41 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-25 13:57 [patch 0/2] per-CPU vmstat thresholds and vmstat worker disablement Marcelo Tosatti
2017-04-25 13:57 ` [patch 1/2] MM: remove unused quiet_vmstat function Marcelo Tosatti
2017-04-25 13:57 ` [patch 2/2] MM: allow per-cpu vmstat_threshold and vmstat_worker configuration Marcelo Tosatti
2017-04-25 19:29 ` Rik van Riel
2017-04-25 19:36 ` Marcelo Tosatti
2017-05-02 14:28 ` Luiz Capitulino
2017-05-02 16:52 ` Marcelo Tosatti
2017-05-02 17:15 ` Luiz Capitulino
2017-05-02 17:21 ` Marcelo Tosatti
2017-05-11 15:37 ` Christoph Lameter
2017-05-12 12:27 ` Marcelo Tosatti
2017-05-12 15:11 ` Christoph Lameter
2017-05-12 15:40 ` Marcelo Tosatti [this message]
2017-05-12 16:03 ` Christoph Lameter
2017-05-12 16:07 ` Christoph Lameter
2017-05-12 16:19 ` Marcelo Tosatti
2017-05-12 16:57 ` Christoph Lameter
2017-05-15 19:15 ` Marcelo Tosatti
2017-05-16 13:37 ` Christoph Lameter
2017-05-19 14:34 ` Marcelo Tosatti
2017-05-19 17:13 ` Christoph Lameter
2017-05-19 17:49 ` Luiz Capitulino
2017-05-22 16:35 ` Christoph Lameter
2017-05-25 19:35 ` Marcelo Tosatti
2017-05-26 3:24 ` Christoph Lameter
2017-05-26 19:09 ` Marcelo Tosatti
2017-05-30 18:17 ` Christoph Lameter
2017-07-10 15:05 ` Marcelo Tosatti
2017-05-20 8:26 ` Marcelo Tosatti
2017-05-22 16:38 ` Christoph Lameter
2017-05-22 21:13 ` Marcelo Tosatti
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