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From: David Marchand <david.marchand@redhat.com>
To: "Mattias Rönnblom" <hofors@lysator.liu.se>
Cc: dev@dpdk.org, thomas@monjalon.net, frode.nordahl@canonical.com,
	mattias.ronnblom@ericsson.com, stable@dpdk.org,
	"Anatoly Burakov" <anatoly.burakov@intel.com>,
	"David Hunt" <david.hunt@intel.com>,
	"Sivaprasad Tummala" <sivaprasad.tummala@amd.com>,
	"Stephen Hemminger" <stephen@networkplumber.org>,
	"Chengwen Feng" <fengchengwen@huawei.com>,
	"Konstantin Ananyev" <konstantin.ananyev@huawei.com>,
	"Morten Brørup" <mb@smartsharesystems.com>
Subject: Re: [PATCH 2/3] power: defer lcore variable allocation
Date: Thu, 12 Dec 2024 08:57:35 +0100	[thread overview]
Message-ID: <CAJFAV8z2pCU+uk=Sv6Cpvt1_JBHjfV2zrNHWGCa5uEw1oohvjQ@mail.gmail.com> (raw)
In-Reply-To: <16f6d334-d999-4fe7-b177-6daf881b8f1e@lysator.liu.se>

On Fri, Dec 6, 2024 at 12:29 PM Mattias Rönnblom <hofors@lysator.liu.se> wrote:
> I would wrap all RTE_LCORE_VAR_LCORE() and RTE_LCORE_VAR().
>
> static struct pmd_core_cfg *
> get_cfg_lcore(unsigned int lcore_id)
> {
>         assure_lcore_cfgs_alloced();
>         return RTE_LCORE_VAR_LCORE(lcore_cfgs, lcore_id);
> }
>
> static struct pmd_core_cfg *
> get_cfg(void)
> {
>         get_cfg_lcore(rte_lcore_id());
> }
>
> Add
>
> static void
> assure_lcore_cfgs_alloced(unsigned int lcore_id)
> {
>         if (lcore_cfgs != NULL)

==

>                 lcore_cfgs_alloc();
> }
>
> ..or maybe better merge assure_lcore_cfgs_alloced() and lcore_cfgs_alloc().
>
> Makes it a little harder to make mistakes.

clb_multiwait, clb_pause and clb_scale_freq callbacks can only be
reached after a successful call to
rte_power_ethdev_pmgmt_queue_enable.
Triggering an allocation in them means we are hiding a (internal)
programatic error as allocation and use of a lcore variable are
clearly separated atm.
If we keep the lcore var api as is, I would add an assert() (maybe
under a debug build option) in RTE_LCORE_VAR macros themselves, as
calling with a NULL handle means the initialisation path in some
code/RTE_LCORE_VAR API use was incorrect.


Or because you propose to add the same type of helpers in both this
patch and the next, I am considering the other way: hide the
allocation in the RTE_LCORE_VAR* macros.
Checking for already allocated var in RTE_LCORE_VAR_ALLOC seems fine.
But the "fast path" RTE_LCORE_VAR would have an unwanted branch in most cases.


> A somewhat unrelated question: why is pmd_core_cfg cache-line aligned? I
> don't think it should be.

Before the conversion to per lcore variable, it was probably useful
(avoiding false sharing).
With the conversion, indeed, it looks like a waste of space.
It seems worth a separate fix.


-- 
David Marchand


  reply	other threads:[~2024-12-12  7:57 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20241205175754.1673888-1-david.marchand@redhat.com>
2024-12-05 17:57 ` [PATCH 1/3] random: defer seeding to EAL init David Marchand
2024-12-06 11:09   ` Mattias Rönnblom
2024-12-16  9:38   ` Burakov, Anatoly
2024-12-05 17:57 ` [PATCH 2/3] power: defer lcore variable allocation David Marchand
2024-12-06 11:29   ` Mattias Rönnblom
2024-12-12  7:57     ` David Marchand [this message]
2024-12-13  6:58       ` Mattias Rönnblom
2024-12-16 10:02         ` David Marchand
2024-12-05 17:57 ` [PATCH 3/3] eal/x86: defer power intrinsics " David Marchand
2024-12-06 11:32   ` Mattias Rönnblom
     [not found] ` <20241217085954.3310414-1-david.marchand@redhat.com>
2024-12-17  8:59   ` [PATCH v2 2/5] random: defer seeding to EAL init David Marchand
2024-12-18 16:35     ` Stephen Hemminger
2024-12-18 17:03       ` Mattias Rönnblom
2024-12-17  8:59   ` [PATCH v2 3/5] power: defer lcore variable allocation David Marchand
2024-12-18 11:17     ` Burakov, Anatoly
2024-12-17  8:59   ` [PATCH v2 5/5] eal/x86: defer power intrinsics " David Marchand
2024-12-18 11:17     ` Burakov, Anatoly

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