Re: [PATCH] eal/linux: redefine the name for rte_fbarray_init()

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 15 Nov 2024 10:26:00 +0800
Zhou congjie <zcjie0802@qq.com> wrote:

> On Thu, 14 Nov 2024, Stephen Hemminger wrote:
> 
> > Date: Fri, 15 Nov 2024 01:06:27
> > From: Stephen Hemminger <stephen@networkplumber.org>
> > To: zcjie0802 <zcjie0802@qq.com>
> > Cc: dev <dev@dpdk.org>, anatoly.burakov <anatoly.burakov@intel.com>
> > Subject: Re: [PATCH] eal/linux: redefine the name for rte_fbarray_init()
> > 
> > What about using thread id instead?
> > 
> > From d1687ffbf865ba0b2d64c35acd602ca43329691e Mon Sep 17 00:00:00 2001
> > From: Stephen Hemminger <stephen@networkplumber.org>
> > Date: Thu, 14 Nov 2024 08:48:54 -0800
> > Subject: [PATCH] eal: fix fbarray name with multiple secondary processes
> > 
> > When multiple secondary processes run in different containers, names
> > identified by PIDs are not unique due to the pid namespace.
> > Add current thread id to the name to be unique.
> > 
> > Fixes: 046aa5c4477b ("mem: add memalloc init stage")
> > Cc: anatoly.burakov@intel.com
> > 
> > Reported-by: Congjie Zhou <zcjie0802@qq.com>
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > ---
> >  lib/eal/linux/eal_memalloc.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/lib/eal/linux/eal_memalloc.c b/lib/eal/linux/eal_memalloc.c
> > index e354efc95d..776260e14f 100644
> > --- a/lib/eal/linux/eal_memalloc.c
> > +++ b/lib/eal/linux/eal_memalloc.c
> > @@ -1447,8 +1447,8 @@ secondary_msl_create_walk(const struct rte_memseg_list *msl,
> >  	local_msl = &local_memsegs[msl_idx];
> >  
> >  	/* create distinct fbarrays for each secondary */
> > -	snprintf(name, RTE_FBARRAY_NAME_LEN, "%s_%i",
> > -		primary_msl->memseg_arr.name, getpid());
> > +	snprintf(name, RTE_FBARRAY_NAME_LEN, "%s_%i_%i",
> > +		 primary_msl->memseg_arr.name, getpid(), rte_sys_gettid());
> >  
> >  	ret = rte_fbarray_init(&local_msl->memseg_arr, name,
> >  		primary_msl->memseg_arr.len,
> >   
> 
> As far as know, the tid is pid independent, so programs in different PID 
> namespaces may have the same pid and tid.
> 
> For the solution that uses a global counter, I feel it can only be 
> implemented by adding variables into rte_config or rte_mem_config, which 
> involves modifying multiple files. Adding the current time would be more 
> simple. This code is excuted only once when the secondary process is created, so 
> it will not cause performance issues.

The combination of thread id and process id will be unique but
there might be issues with some container implementations which will
have overlapping pid's (see Docker --pid flag).

The TSC is available in all of DPDK via rte_get_tsc_cycles()
or use rte_get_timer_cycles().

But you could still have collisions from two containers using hidden pid
doing function at same exact time. Not ever likely, but it is possible.