From: Thomas Monjalon <thomas.monjalon@6wind.com>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Cc: "Pattan, Reshma" <reshma.pattan@intel.com>, dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx callback lists
Date: Wed, 15 Jun 2016 13:17:32 +0200 [thread overview]
Message-ID: <3682885.ZONGT1nz9t@xps13> (raw)
In-Reply-To: <2601191342CEEE43887BDE71AB97725836B7164D@irsmsx105.ger.corp.intel.com>
2016-06-15 09:54, Ananyev, Konstantin:
>
> > -----Original Message-----
> > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > Sent: Wednesday, June 15, 2016 9:49 AM
> > To: Ananyev, Konstantin
> > Cc: Pattan, Reshma; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx callback lists
> >
> > 2016-06-15 08:37, Ananyev, Konstantin:
> > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > 2016-06-15 05:30, Pattan, Reshma:
> > > > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > > > 2016-06-14 10:38, Reshma Pattan:
> > > > > > > Added spinlocks around add/remove logic of Rx and Tx callbacks to
> > > > > > > avoid corruption of callback lists in multithreaded context.
> > > > > > >
> > > > > > > Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
> > > > > >
> > > > > > Why cb->next is not locked in burst functions?
> > > > > It is safe to do "read access" here and doesn't require any locking as rx/tx burst is initiated by only local user(control plane)
> > thread.
> > > > >
> > > > > > Just protecting add/remove but not its usage seems useless.
> > > > > Here locks were required around add/remove to protect "write access" because write to callback list is now done from 2
> > threads
> > > > > i.e. one from local user thread(control plane) and another from pdump control thread(initiated by remote pdump request).
> > > >
> > > > So read and write can be done by different threads.
> > >
> > > Yes, and this is possible even in current DPDK version (16.04).
> > > What is added by Reshma's patch - now it is possible to have concurrent write
> > > from 2 different thread to that list.
> > >
> > > > I think the read access would need locking but we do not want it
> > > > in fast path.
> > >
> > > I don't think it would be needed.
> > > As I said - read/write interaction didn't change from what we have right now.
> > > But if you have some particular scenario in mind that you believe would cause
> > > a race condition - please speak up.
> >
> > If we add/remove a callback during a burst? Is it possible that the next
> > pointer would have a wrong value leading to a crash?
> > Maybe we need a comment to state that we should not alter burst
> > callbacks while running burst functions.
>
> Current status (16.04):
> It is safe to add/remove RX/TX callbacks while
> another thread is doing simultaneously RX/TX burst over same queue.
> I.E: it is supposed to be safe to invoke
> rte_eth_add(/remove)_rx(/tx)_callback() and rte_eth_rx_burst()/rte_eth_tx_burst()
> from different threads simultaneously.
> Though it is not safe to free/modify that rte_eth_rxtx_callback while current
> rte_eth_rx_burst()/rte_eth_tx_burst() are still active.
> That exactly what comments for rte_eth_remove_rx_callback() say:
>
> * Note: the callback is removed from the callback list but it isn't freed
> * since the it may still be in use. The memory for the callback can be
> * subsequently freed back by the application by calling rte_free():
> *
> * - Immediately - if the port is stopped, or the user knows that no
> * callbacks are in flight e.g. if called from the thread doing RX/TX
> * on that queue.
> *
> * - After a short delay - where the delay is sufficient to allow any
> * in-flight callbacks to complete.
>
> In other words, right now there only way to know for sure that it is safe
> to free the removed callback - is to stop the port.
>
> Does it need to be changed, so when rte_eth_remove_rx_callback() returns
> user can safely free the callback (or even better rte_eth_remove_rx_callback free the callback for us)?
> In my opinion - yes.
> Though, I think, it has nothing to do with pdump patches, and I think should be a matter
> for separate a patch/discussion.
>
> Now with pdump library introduction - there is possibility that 2 different threads
> can try to add/remove callbacks for the same queue simultaneously.
> First one - thread executing control requests from local user,
> second one - pdump control thread executing pdump requests from pdump client.
> That lock is introduced to avoid race condition between such 2 threads:
> i.e. to prevent multiple threads to modify same list simultaneously.
> It is not intended to synchronise read/write accesses to the list, see above.
OK thanks for the explanations
next prev parent reply other threads:[~2016-06-15 11:17 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1465487895-5870-1-git-send-email-reshma.pattan@intel.com>
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 0/8] add packet capture framework Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 1/8] librte_ether: protect add/remove of rxtx callbacks with spinlocks Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 2/8] librte_ether: add new api rte_eth_add_first_rx_callback Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 3/8] librte_ether: add new fields to rte_eth_dev_info struct Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 4/8] librte_ether: make rte_eth_dev_get_port_by_name rte_eth_dev_get_name_by_port public Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 5/8] lib/librte_pdump: add new library for packet capturing support Reshma Pattan
2016-06-10 18:48 ` Aaron Conole
2016-06-10 22:14 ` Pattan, Reshma
2016-06-13 13:28 ` Aaron Conole
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 6/8] app/pdump: add pdump tool for packet capturing Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 7/8] app/test-pmd: add pdump initialization uninitialization Reshma Pattan
2016-06-10 16:18 ` [dpdk-dev] [PATCH v8 8/8] doc: update doc for packet capture framework Reshma Pattan
2016-06-10 23:23 ` [dpdk-dev] [PATCH v8 0/8] add " Neil Horman
2016-06-13 8:47 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 " Reshma Pattan
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 1/8] ethdev: use locks to protect Rx/Tx callback lists Reshma Pattan
2016-06-14 19:59 ` Thomas Monjalon
2016-06-15 5:30 ` Pattan, Reshma
2016-06-15 8:19 ` Thomas Monjalon
2016-06-15 8:37 ` Ananyev, Konstantin
2016-06-15 8:48 ` Thomas Monjalon
2016-06-15 9:54 ` Ananyev, Konstantin
2016-06-15 11:17 ` Thomas Monjalon [this message]
2016-06-15 13:49 ` Thomas Monjalon
2016-06-15 12:15 ` Ivan Boule
2016-06-15 12:40 ` Ananyev, Konstantin
2016-06-15 13:29 ` Bruce Richardson
2016-06-15 14:07 ` Ivan Boule
2016-06-15 14:19 ` Bruce Richardson
2016-06-15 14:20 ` Ananyev, Konstantin
2016-06-15 14:22 ` Bruce Richardson
2016-06-15 14:27 ` Ananyev, Konstantin
2016-06-15 15:33 ` Ivan Boule
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 2/8] ethdev: add new api to add Rx callback as head of the list Reshma Pattan
2016-06-14 20:01 ` Thomas Monjalon
2016-06-14 21:43 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 3/8] ethdev: add new fields to ethdev info struct Reshma Pattan
2016-06-14 20:10 ` Thomas Monjalon
2016-06-14 21:57 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 4/8] ethdev: make get port by name and get name by port public Reshma Pattan
2016-06-14 20:23 ` Thomas Monjalon
2016-06-14 21:55 ` Pattan, Reshma
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 5/8] pdump: add new library for packet capturing support Reshma Pattan
2016-06-14 20:28 ` Thomas Monjalon
2016-06-14 21:59 ` Pattan, Reshma
2016-06-15 9:05 ` Mcnamara, John
2016-06-15 9:32 ` Thomas Monjalon
2016-06-15 9:43 ` Bruce Richardson
2016-06-15 15:44 ` Mcnamara, John
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 6/8] app/pdump: add pdump tool for packet capturing Reshma Pattan
2016-06-14 19:56 ` Thomas Monjalon
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 7/8] app/testpmd: add pdump initialization uninitialization Reshma Pattan
2016-06-14 9:38 ` [dpdk-dev] [PATCH v9 8/8] doc: update doc for packet capture framework Reshma Pattan
2016-06-14 20:41 ` Thomas Monjalon
2016-06-15 5:44 ` Pattan, Reshma
2016-06-15 8:24 ` Thomas Monjalon
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 0/7] add " Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 1/7] ethdev: use locks to protect Rx/Tx callback lists Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 2/7] ethdev: add new api to add Rx callback as head of the list Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 3/7] ethdev: add new fields to ethdev info struct Reshma Pattan
2016-06-16 19:14 ` Thomas Monjalon
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 4/7] ethdev: make get port by name and get name by port public Reshma Pattan
2016-06-16 20:27 ` Thomas Monjalon
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 5/7] pdump: add new library for packet capturing support Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 6/7] app/pdump: add pdump tool for packet capturing Reshma Pattan
2016-06-15 14:06 ` [dpdk-dev] [PATCH v10 7/7] app/testpmd: add pdump initialization uninitialization Reshma Pattan
2016-06-16 21:55 ` [dpdk-dev] [PATCH v10 0/7] add packet capture framework Thomas Monjalon
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