From: Stephen Hemminger <stephen@networkplumber.org>
To: Ferruh Yigit <ferruh.yigit@amd.com>
Cc: "John W. Linville" <linville@tuxdriver.com>,
"Thomas Monjalon" <thomas@monjalon.net>,
dev@dpdk.org, "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
"Morten Brørup" <mb@smartsharesystems.com>,
"Honnappa Nagarahalli" <Honnappa.Nagarahalli@arm.com>
Subject: Re: [RFC v3] net/af_packet: make stats reset reliable
Date: Tue, 7 May 2024 07:52:51 -0700 [thread overview]
Message-ID: <20240507075251.144e91b7@hermes.local> (raw)
In-Reply-To: <44f2d6b8-9b38-4e1f-9d9a-46d719532808@amd.com>
On Tue, 7 May 2024 14:48:51 +0100
Ferruh Yigit <ferruh.yigit@amd.com> wrote:
> On 5/3/2024 11:00 PM, Stephen Hemminger wrote:
> > On Fri, 3 May 2024 16:45:47 +0100
> > Ferruh Yigit <ferruh.yigit@amd.com> wrote:
> >
> >> For stats reset, use an offset instead of zeroing out actual stats values,
> >> get_stats() displays diff between stats and offset.
> >> This way stats only updated in datapath and offset only updated in stats
> >> reset function. This makes stats reset function more reliable.
> >>
> >> As stats only written by single thread, we can remove 'volatile' qualifier
> >> which should improve the performance in datapath.
> >>
> >> While updating around, 'igb_stats' parameter renamed as 'stats'.
> >>
> >> Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
> >> ---
> >> Cc: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> >> Cc: Stephen Hemminger <stephen@networkplumber.org>
> >> Cc: Morten Brørup <mb@smartsharesystems.com>
> >>
> >> This update triggered by mail list discussion [1].
> >>
> >> [1]
> >> https://inbox.dpdk.org/dev/3b2cf48e-2293-4226-b6cd-5f4dd3969f99@lysator.liu.se/
> >
> >
> > NAK
> >
> > I did not hear a good argument why atomic or volatile was necessary in the first place.
> > Why?
> >
>
> Sure, the patch is done as RFC intentionally to discuss the approach.
>
> Agree that volatile and atomics (fetch + add + store) is not required
> for thread synchronization, as only one CPU updates stats.
> Even this understanding is important because there are PMDs using full
> atomics for stats update, like null PMD [1], this will help up clear them.
>
>
> And there is a case, stats reset and stats updated in different threads
> simultaneously, for this 'volatile' is not sufficient anyway and full
> atomics is required. As this will cause performance impact we are
> already saying stats update and reset can't happen at the same time [2].
> With this update volatile and atomics are not required for this case too.
> (Also using offset to increase stats reset reliability.)
>
>
> In this patch volatile replaced with atomic load and atomic store (not
> atomic fetch and add), to ensure that stats stored to memory and not
> kept in device registers only.
> With volatile, it is guaranteed that updated stats stored back to
> memory, but without volatile and atomics I am not sure if this is
> guaranteed. Practically I can see this working, but theoretically not
> sure. This is similar concern with change in your patch that is casting
> to volatile to ensure value read from memory [3].
>
> Expectation is, only atomics load and store will have smaller
> performance impact than volatile, ensuring memory load and store when
> needed.
The device register worry, can just be handled with a compiler barrier.
Does not need the stronger guarantee of atomic or volatile.
next prev parent reply other threads:[~2024-05-07 14:52 UTC|newest]
Thread overview: 134+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-25 17:46 [RFC] " Ferruh Yigit
2024-04-26 11:33 ` Morten Brørup
2024-04-26 13:37 ` Ferruh Yigit
2024-04-26 14:56 ` Morten Brørup
2024-04-28 15:42 ` Mattias Rönnblom
2024-04-26 14:38 ` [RFC v2] " Ferruh Yigit
2024-04-26 14:47 ` Morten Brørup
2024-04-28 15:11 ` Mattias Rönnblom
2024-05-01 16:19 ` Ferruh Yigit
2024-05-02 5:51 ` Mattias Rönnblom
2024-05-02 14:22 ` Ferruh Yigit
2024-05-02 15:59 ` Stephen Hemminger
2024-05-02 18:20 ` Ferruh Yigit
2024-05-02 17:37 ` Mattias Rönnblom
2024-05-02 18:26 ` Stephen Hemminger
2024-05-02 21:26 ` Mattias Rönnblom
2024-05-02 21:46 ` Stephen Hemminger
2024-05-07 7:23 ` Mattias Rönnblom
2024-05-07 13:49 ` Ferruh Yigit
2024-05-07 14:51 ` Stephen Hemminger
2024-05-07 16:00 ` Morten Brørup
2024-05-07 16:54 ` Ferruh Yigit
2024-05-07 18:47 ` Stephen Hemminger
2024-05-08 7:48 ` Mattias Rönnblom
2024-05-08 6:28 ` Mattias Rönnblom
2024-05-08 6:25 ` Mattias Rönnblom
2024-05-07 19:19 ` Morten Brørup
2024-05-08 6:34 ` Mattias Rönnblom
2024-05-08 7:10 ` Morten Brørup
2024-05-08 7:23 ` Mattias Rönnblom
2024-04-26 21:28 ` [RFC] " Patrick Robb
2024-05-03 15:45 ` [RFC v3] " Ferruh Yigit
2024-05-03 22:00 ` Stephen Hemminger
2024-05-07 13:48 ` Ferruh Yigit
2024-05-07 14:52 ` Stephen Hemminger [this message]
2024-05-07 17:27 ` Ferruh Yigit
2024-05-08 7:19 ` Mattias Rönnblom
2024-05-08 15:23 ` Stephen Hemminger
2024-05-08 19:48 ` Ferruh Yigit
2024-05-08 20:54 ` Stephen Hemminger
2024-05-09 7:43 ` Morten Brørup
2024-05-09 9:29 ` Bruce Richardson
2024-05-09 11:37 ` Morten Brørup
2024-05-09 14:19 ` Morten Brørup
2024-05-10 4:56 ` Stephen Hemminger
2024-05-10 9:14 ` Morten Brørup
2024-05-07 15:27 ` Morten Brørup
2024-05-07 17:40 ` Ferruh Yigit
2024-05-10 5:01 ` [RFC 0/3] generic sw counters Stephen Hemminger
2024-05-10 5:01 ` [RFC 1/3] ethdev: add internal helper of SW driver statistics Stephen Hemminger
2024-05-10 5:01 ` [RFC 2/3] net/af_packet: use SW stats helper Stephen Hemminger
2024-05-10 5:01 ` [RFC 3/3] net/tap: use generic SW stats Stephen Hemminger
2024-05-10 17:29 ` [RFC 0/3] generic sw counters Morten Brørup
2024-05-10 19:30 ` Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 0/7] generic SW counters Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 1/7] eal: generic 64 bit counter Stephen Hemminger
2024-05-13 19:36 ` Morten Brørup
2024-05-13 18:52 ` [RFC v2 2/7] ethdev: add internal helper of SW driver statistics Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 3/7] net/af_packet: use SW stats helper Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 4/7] net/tap: use generic SW stats Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 5/7] net/pcap: " Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 6/7] net/af_xdp: " Stephen Hemminger
2024-05-13 18:52 ` [RFC v2 7/7] net/ring: " Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 0/7] Generic SW counters Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 1/7] eal: generic 64 bit counter Stephen Hemminger
2024-05-15 9:30 ` Morten Brørup
2024-05-15 15:03 ` Stephen Hemminger
2024-05-15 16:18 ` Morten Brørup
2024-05-14 15:35 ` [PATCH v3 2/7] ethdev: add internal helper of SW driver statistics Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 3/7] net/af_packet: use SW stats helper Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 4/7] net/af_xdp: use generic SW stats Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 5/7] net/pcap: " Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 6/7] net/ring: " Stephen Hemminger
2024-05-14 15:35 ` [PATCH v3 7/7] net/tap: " Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 0/8] Generic 64 bit counters for SW PMD's Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 1/8] eal: generic 64 bit counter Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 2/8] ethdev: add common counters for statistics Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 3/8] net/af_packet: use generic SW stats Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 4/8] net/af_xdp: " Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 5/8] net/pcap: " Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 6/8] net/ring: " Stephen Hemminger
2024-05-15 23:40 ` [PATCH v4 7/8] net/tap: " Stephen Hemminger
2024-05-15 23:41 ` [PATCH v4 8/8] net/null: " Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 0/9] Generic 64 bit counters Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 1/9] eal: generic 64 bit counter Stephen Hemminger
2024-05-16 18:22 ` Wathsala Wathawana Vithanage
2024-05-16 21:42 ` Stephen Hemminger
2024-05-17 2:39 ` Honnappa Nagarahalli
2024-05-17 3:29 ` Stephen Hemminger
2024-05-17 4:39 ` Honnappa Nagarahalli
2024-05-16 15:40 ` [PATCH v5 2/9] ethdev: add common counters for statistics Stephen Hemminger
2024-05-16 18:30 ` Wathsala Wathawana Vithanage
2024-05-17 0:19 ` Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 3/9] net/af_packet: use generic SW stats Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 4/9] net/af_xdp: " Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 5/9] net/pcap: " Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 6/9] test/pmd_ring: initialize mbufs Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 7/9] net/ring: use generic SW stats Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 8/9] net/tap: " Stephen Hemminger
2024-05-16 15:40 ` [PATCH v5 9/9] net/null: " Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 0/9] Generic 64 bit counters for SW drivers Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 1/9] eal: generic 64 bit counter Stephen Hemminger
2024-05-17 2:45 ` Honnappa Nagarahalli
2024-05-17 3:30 ` Stephen Hemminger
2024-05-17 4:26 ` Honnappa Nagarahalli
2024-05-17 6:44 ` Morten Brørup
2024-05-17 15:05 ` Stephen Hemminger
2024-05-17 16:18 ` Stephen Hemminger
2024-05-18 14:00 ` Morten Brørup
2024-05-19 15:13 ` Stephen Hemminger
2024-05-19 17:10 ` Morten Brørup
2024-05-19 22:49 ` Stephen Hemminger
2024-05-20 7:57 ` Morten Brørup
2024-05-17 15:07 ` Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 2/9] ethdev: add common counters for statistics Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 3/9] net/af_packet: use generic SW stats Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 4/9] net/af_xdp: " Stephen Hemminger
2024-05-17 13:34 ` Loftus, Ciara
2024-05-17 14:54 ` Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 5/9] net/pcap: " Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 6/9] test/pmd_ring: initialize mbufs Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 7/9] net/ring: use generic SW stats Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 8/9] net/tap: " Stephen Hemminger
2024-05-17 0:12 ` [PATCH v6 9/9] net/null: " Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 0/9] Use weak atomic operations for SW PMD counters Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 1/9] eal: generic 64 bit counter Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 2/9] ethdev: add common counters for statistics Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 3/9] net/af_packet: use generic SW stats Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 4/9] net/af_xdp: " Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 5/9] net/pcap: " Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 6/9] test/pmd_ring: initialize mbufs Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 7/9] net/ring: use generic SW stats Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 8/9] net/tap: " Stephen Hemminger
2024-05-17 17:35 ` [PATCH v7 9/9] net/null: " Stephen Hemminger
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