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Date: Thu, 10 Jul 2025 07:37:47 -0700
From: Andre Muezerie <andremue@linux.microsoft.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: dev@dpdk.org, Konstantin Ananyev <konstantin.ananyev@huawei.com>,
 David Marchand <david.marchand@redhat.com>,
 Bruce Richardson <bruce.richardson@intel.com>, honnappa.nagarahalli@arm.com
Subject: Re: [PATCH] rcu: add deprecation notice about limit on defer queue
 element size
Message-ID: <20250710143747.GA24344@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
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 <4620749.daG60p0z9X@thomas>
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On Tue, Jul 01, 2025 at 04:17:20PM +0200, Thomas Monjalon wrote:
> 23/05/2025 01:37, Andre Muezerie:
> > The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim establish
> > no limit on the size of each element in the defer queue.
> 
> Very good, we need more unlimited API in DPDK.
> 
> > With DPDK 25.11 a hard limit will be set (``RTE_QSBR_ESIZE_MAX``).
> 
> I think it is a step in the wrong direction.
> I prefer having no limit.
> 
> > This will allow fixed C arrays to be used in the functions' implementations,
> > avoiding VLAs and use of alloca().
> 
> I don't understand this justification.
> Why trying to remove the 2 alloca() in the lib RCU?
> 

Only because other developer expressed concerns that using alloca() allows
ill-intended callers to cause a stack overflow.
I personally also prefer to have no hardcoded limits.