Re: [RFC] eal: RFC to refactor rte_eal_init into sub-functions

[Thomas Monjalon <thomas@monjalon.net>]

08/11/2023 12:51, Bruce Richardson:
> On Thu, Nov 02, 2023 at 11:19:24AM -0700, Rahul Gupta wrote:
> > From: Rahul Gupta <rahulgupt@microsoft.com>
> > 
> > Initialization often requires rte_eal_init + rte_pktmbuf_pool_create
> > which can consume a total time of 500-600 ms:
> > a) For many devices FLR may take a significant chunk of time
> >    (200-250 ms in our use-case), this FLR is triggered during device
> >    probe in rte_eal_init().
> > b) rte_pktmbuf_pool_create() can consume upto 300-350 ms for
> > applications that require huge memory.
> > 
> > This cost is incurred on each restart (which happens in our use-case
> > during binary updates for servicing).
> > This patch provides an optimization using pthreads that appplications
> > can use and which can save 200-230ms.
> > 
> > In this patch, rte_eal_init() is refactored into two parts-
> > a) 1st part is dependent code ie- it’s a perquisite of the FLR and
> >    mempool creation. So this code needs to be executed before any
> >    pthreads. Its named as rte_eal_init_setup()
> > b) 2nd part of code is independent code ie- it can execute in parallel
> >    to mempool creation in a pthread. Its named as rte_probe_and_ioctl().
> > 
> > Existing applications require no changes unless they wish to leverage
> > the optimization.
> > 
> > If the application wants to use pthread functionality, it should call-
> > a) rte_eal_init_setup() then create two or more pthreads-
> > b) in one pthread call- rte_probe_and_ioctl(),
> > c) second pthread call- rte_pktmbuf_pool_create()
> > d) (optional) Other pthreads for  any other independent function.
> > 
> > Signed-off-by: Rahul Gupta <rahulgupt@linux.microsoft.com>
> 
> Reading the description, this seems an interesting idea, and a good saving.
> 
> If I may, I wonder if I can suggest a slight alternative. Rather than
> splitting EAL init into two functions like that, how about providing an
> "rte_eal_init_async()" function, which does part 1, and then spawns a
> thread for part 2, before returning. We can then provide an
> rte_eal_init_done() [or eal_init_async_done()] function to allow apps to
> resync and check for EAL being done.
> 
> The reason for suggesting this is that the naming and purpose of the APIs
> may be a little clearer for the end user. Allowing the async init function
> to create threads also allows possible future parallelism in the function
> itself. For example, we could do probing of the devices themselves in
> parallel.

I like the idea of async init.