From: Olivier MATZ <olivier.matz@6wind.com>
To: "Hanoch Haim (hhaim)" <hhaim@cisco.com>
Cc: Konstantin Ananyev <konstantin.ananyev@intel.com>,
Ilya Matveychikov <matvejchikov@gmail.com>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v3] mbuf: cleanup rte_pktmbuf_lastseg(), fix atomic usage
Date: Thu, 16 Nov 2017 09:42:04 +0100 [thread overview]
Message-ID: <20171116084112.ockgmxnxews7coie@platinum> (raw)
In-Reply-To: <2fa9a7806c9e447995d6017c6def9894@XCH-RTP-017.cisco.com>
Hi Hanoh,
On Thu, Nov 16, 2017 at 07:16:31AM +0000, Hanoch Haim (hhaim) wrote:
> Hi Oliver,
>
> It's hard for me to follow this thread.
Yes, here are some few tips to make it easier to follow:
- avoid top-posting
- prefix quoted lines with "> "
- describe the problem and how you solve it in the commit log
- one problem = one patch
> 1) It is not about clear/not-clear, it is error prone to *replicate* code that has the same logic.
>
> "I'm not convinced that:
>
> __rte_pktmbuf_reset_nb_segs(m);
>
> is clearer than:
>
> m->next = NULL;
> m->nb_segs = 1;
>
> Anyway, I agree this should not be part of this patch. We should only keep the fix.
> "
rte_mbuf_refcnt_update() was not used in rte_pktmbuf_prefree_seg() to
avoid reading the refcount twice.
The problem of having clear or unclear is fundamental. I don't see the point of
having a function __rte_pktmbuf_reset_nb_segs(). Keeping the two affectations
makes things explicit.
> 2) This definitely does not look good.
> All the point in my patch is to move the ref-cnt operations to set of API that already taking care of RTE_MBUF_REFCNT_ATOMIC
>
> + /* We don't use rte_mbuf_refcnt_update() because we already
> + * tested that refcnt != 1.
> + */
> +#ifdef RTE_MBUF_REFCNT_ATOMIC
> + ret = rte_atomic16_add_return(&m->refcnt_atomic, -1);
> +#else
> + ret = --m->refcnt;
> +#endif
> + if (ret != 0)
> + return NULL;
>
We cannot use the existing API taking care of atomic refcount
rte_mbuf_refcnt_update() because it would read the refcount twice.
We cannot change the behavior of rte_mbuf_refcnt_update() because it's a
public API.
An option proposed by Konstantin is to introduce a new helper
rte_mbuf_refcnt_update_blind() that does the same than
rte_mbuf_refcnt_update() but without the first test. It think it is a
bit overkill to have this function for one caller.
That's why I end up with this patch. I don't see why it would be an
issue to have a mbuf ifdef inside the mbuf code.
Olivier
next prev parent reply other threads:[~2017-11-16 8:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-15 9:14 Hanoh Haim
2017-11-15 11:13 ` Ilya Matveychikov
2017-11-15 12:46 ` Hanoch Haim (hhaim)
2017-11-15 17:30 ` Olivier MATZ
2017-11-16 7:16 ` Hanoch Haim (hhaim)
2017-11-16 8:07 ` Ilya Matveychikov
2017-11-16 8:42 ` Olivier MATZ [this message]
2017-11-16 9:06 ` Hanoch Haim (hhaim)
2017-11-16 9:32 ` Ilya Matveychikov
2017-11-16 9:37 ` Olivier MATZ
2017-11-16 9:44 ` Ilya Matveychikov
2017-11-16 10:54 ` Ananyev, Konstantin
2017-12-08 15:46 ` [dpdk-dev] [PATCH v4] mbuf: fix mbuf free performance with non atomic refcnt Olivier Matz
2017-12-08 16:04 ` Ilya Matveychikov
2017-12-08 16:19 ` Olivier MATZ
2017-12-08 16:37 ` Stephen Hemminger
2017-12-10 8:37 ` Hanoch Haim (hhaim)
2017-12-11 10:28 ` Olivier MATZ
2018-01-18 23:23 ` Thomas Monjalon
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