From: Olivier Matz <olivier.matz@6wind.com>
To: Lazaros Koromilas <l@nofutznetworks.com>, dev@dpdk.org
Cc: Thomas Monjalon <thomas.monjalon@6wind.com>
Subject: Re: [dpdk-dev] [PATCH v2] ring: check for zero objects mc dequeue / mp enqueue
Date: Fri, 25 Mar 2016 12:15:23 +0100 [thread overview]
Message-ID: <56F51DCB.5020502@6wind.com> (raw)
In-Reply-To: <1458229783-15547-1-git-send-email-l@nofutznetworks.com>
Hi Lazaros,
On 03/17/2016 04:49 PM, Lazaros Koromilas wrote:
> Issuing a zero objects dequeue with a single consumer has no effect.
> Doing so with multiple consumers, can get more than one thread to succeed
> the compare-and-set operation and observe starvation or even deadlock in
> the while loop that checks for preceding dequeues. The problematic piece
> of code when n = 0:
>
> cons_next = cons_head + n;
> success = rte_atomic32_cmpset(&r->cons.head, cons_head, cons_next);
>
> The same is possible on the enqueue path.
Just a question about this patch (that has been applied). Thomas
retitled the commit from your log message:
ring: fix deadlock in zero object multi enqueue or dequeue
http://dpdk.org/browse/dpdk/commit/?id=d0979646166e
I think this patch does not fix a deadlock, or did I miss something?
As explained in the following links, the ring may not perform well
if several threads running on the same cpu use it:
http://dpdk.org/ml/archives/dev/2013-November/000714.html
http://www.dpdk.org/ml/archives/dev/2014-January/001070.html
http://www.dpdk.org/ml/archives/dev/2014-January/001162.html
http://dpdk.org/ml/archives/dev/2015-July/020659.html
A deadlock could occur if the threads running on the same core
have different priority.
Regards,
Olivier
next prev parent reply other threads:[~2016-03-25 11:15 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-17 15:49 Lazaros Koromilas
2016-03-17 16:09 ` Mauricio Vásquez
2016-03-18 10:18 ` Bruce Richardson
2016-03-18 10:27 ` Olivier Matz
2016-03-18 10:35 ` Bruce Richardson
2016-03-18 10:35 ` Thomas Monjalon
2016-03-18 12:47 ` Mauricio Vásquez
2016-03-18 14:16 ` Bruce Richardson
2016-03-21 17:47 ` Xie, Huawei
2016-03-22 10:13 ` Bruce Richardson
2016-03-22 14:38 ` Xie, Huawei
2016-03-21 12:23 ` Olivier Matz
2016-03-22 16:49 ` Thomas Monjalon
2016-03-25 11:15 ` Olivier Matz [this message]
2016-03-28 15:48 ` Lazaros Koromilas
2016-03-29 8:54 ` Bruce Richardson
2016-03-29 15:29 ` Olivier MATZ
2016-03-29 16:04 ` Bruce Richardson
2016-03-29 17:35 ` Lazaros Koromilas
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