From: Stephen Hemminger <stephen@networkplumber.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org, tglx@linutronix.de,
Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [RFC] virtio_net: add local_bh_disable() around u64_stats_update_begin
Date: Tue, 16 Oct 2018 11:44:14 -0700 [thread overview]
Message-ID: <20181016114414.23ea73c3@xeon-e3> (raw)
In-Reply-To: <20181016184206.coukhtgmlr32hyl7@linutronix.de>
On Tue, 16 Oct 2018 20:42:07 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> On 2018-10-16 11:01:14 [-0700], Stephen Hemminger wrote:
> > On Tue, 16 Oct 2018 18:55:45 +0200
> > Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> >
> > > Also, ptr->var++ is not an atomic operation even on 64bit CPUs. Which
> > > means if try_fill_recv() runs on CPU0 (via virtnet_receive()) then the
> > > worker might run on CPU1.
> >
> > On modern CPU's increment of native types is atomic but not locked.
> > u64_stats_update_begin is a no-op on UP and also if BIT_PER_LONG != 32
>
> On ARM64 you have load, inc, store. So if two CPUs increment the counter
> simultaneously we might lose one increment. That is why I asked if we
> care or not.
>
> Sebastian
The point is that kicks is just a counter, not important as part of the
device operation. The point of the u64_stats is to avoid problems with
high/low 32 bit wrap on increment. So this is ok on ARM64.
next prev parent reply other threads:[~2018-10-17 2:36 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-16 16:55 [RFC] virtio_net: add local_bh_disable() around u64_stats_update_begin Sebastian Andrzej Siewior
2018-10-16 17:59 ` Stephen Hemminger
2018-10-16 18:21 ` Sebastian Andrzej Siewior
2018-10-16 18:01 ` Stephen Hemminger
2018-10-16 18:42 ` Sebastian Andrzej Siewior
2018-10-16 18:44 ` Stephen Hemminger [this message]
2018-10-18 8:43 ` [PATCH] " Sebastian Andrzej Siewior
2018-10-18 9:06 ` Toshiaki Makita
2018-10-18 9:11 ` Sebastian Andrzej Siewior
2018-10-18 9:26 ` Toshiaki Makita
2018-10-18 23:23 ` David Miller
2018-10-19 2:19 ` Jason Wang
2018-10-17 1:13 ` [RFC] " Toshiaki Makita
2018-10-17 6:48 ` Jason Wang
2018-10-18 8:47 ` Sebastian Andrzej Siewior
2018-10-18 9:00 ` Toshiaki Makita
2018-10-18 9:08 ` Sebastian Andrzej Siewior
2018-10-18 9:19 ` Toshiaki Makita
2018-10-18 9:30 ` Sebastian Andrzej Siewior
2018-10-18 9:53 ` Toshiaki Makita
2018-10-18 13:21 ` Rafael David Tinoco
2018-10-19 2:17 ` Jason Wang
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