Re: [dpdk-dev] [PATCH v4 08/17] eal: apply affinity of EAL thread by assigned cpuset

["Liang, Cunming" <cunming.liang@intel.com>]

> -----Original Message-----
> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
> Sent: Monday, February 09, 2015 4:01 AM
> To: Liang, Cunming; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v4 08/17] eal: apply affinity of EAL thread by
> assigned cpuset
> 
> Hi,
> 
> On 02/02/2015 03:02 AM, Cunming Liang wrote:
> > EAL threads use assigned cpuset to set core affinity during startup.
> > It keeps 1:1 mapping, if no '--lcores' option is used.
> >
> > [...]
> >
> >  lib/librte_eal/bsdapp/eal/eal.c          | 13 ++++---
> >  lib/librte_eal/bsdapp/eal/eal_thread.c   | 63 +++++++++---------------------
> >  lib/librte_eal/linuxapp/eal/eal.c        |  7 +++-
> >  lib/librte_eal/linuxapp/eal/eal_thread.c | 67 +++++++++++---------------------
> >  4 files changed, 54 insertions(+), 96 deletions(-)
> >
> > diff --git a/lib/librte_eal/bsdapp/eal/eal.c b/lib/librte_eal/bsdapp/eal/eal.c
> > index 69f3c03..98c5a83 100644
> > --- a/lib/librte_eal/bsdapp/eal/eal.c
> > +++ b/lib/librte_eal/bsdapp/eal/eal.c
> > @@ -432,6 +432,7 @@ rte_eal_init(int argc, char **argv)
> >  	int i, fctret, ret;
> >  	pthread_t thread_id;
> >  	static rte_atomic32_t run_once = RTE_ATOMIC32_INIT(0);
> > +	char cpuset[CPU_STR_LEN];
> >
> >  	if (!rte_atomic32_test_and_set(&run_once))
> >  		return -1;
> > @@ -502,13 +503,17 @@ rte_eal_init(int argc, char **argv)
> >  	if (rte_eal_pci_init() < 0)
> >  		rte_panic("Cannot init PCI\n");
> >
> > -	RTE_LOG(DEBUG, EAL, "Master core %u is ready (tid=%p)\n",
> > -		rte_config.master_lcore, thread_id);
> > -
> >  	eal_check_mem_on_local_socket();
> >
> >  	rte_eal_mcfg_complete();
> >
> > +	eal_thread_init_master(rte_config.master_lcore);
> > +
> > +	eal_thread_dump_affinity(cpuset, CPU_STR_LEN);
> > +
> > +	RTE_LOG(DEBUG, EAL, "Master lcore %u is ready (tid=%p;cpuset=[%s])\n",
> > +		rte_config.master_lcore, thread_id, cpuset);
> > +
> >  	if (rte_eal_dev_init() < 0)
> >  		rte_panic("Cannot init pmd devices\n");
> >
> > @@ -532,8 +537,6 @@ rte_eal_init(int argc, char **argv)
> >  			rte_panic("Cannot create thread\n");
> >  	}
> >
> > -	eal_thread_init_master(rte_config.master_lcore);
> > -
> >  	/*
> >  	 * Launch a dummy function on all slave lcores, so that master lcore
> >  	 * knows they are all ready when this function returns.
> 
> I wonder if changing this may have an impact on third-party drivers
> that already use a management thread. Before the patch, the init()
> function of the external library was called with default affinities,
> and now it's called with the affinity from master lcore.
> 
> I think it should at least be noticed in the commit log.
> 
> Why are you doing this change? (I don't say it's a bad change, but
> I don't understand why you are doing it here)
[LCM] To be honest, the main purpose is I don't found any reason to have linuxapp and freebsdapp in different init sequence.
I means in linux it init_master before dev_init(), but in freebsd it reverse.
And as the default value of TLS already changes, if dev_init() first and using those TLS, the result will be not in an EAL thread.
But actually they're in the EAL master thread. So I prefer to do the change follows linuxapp sequence.
> 
> 
> > diff --git a/lib/librte_eal/bsdapp/eal/eal_thread.c
> b/lib/librte_eal/bsdapp/eal/eal_thread.c
> > index d0c077b..5b16302 100644
> > --- a/lib/librte_eal/bsdapp/eal/eal_thread.c
> > +++ b/lib/librte_eal/bsdapp/eal/eal_thread.c
> > @@ -103,55 +103,27 @@ eal_thread_set_affinity(void)
> >  {
> >  	int s;
> >  	pthread_t thread;
> > -
> > -/*
> > - * According to the section VERSIONS of the CPU_ALLOC man page:
> > - *
> > - * The CPU_ZERO(), CPU_SET(), CPU_CLR(), and CPU_ISSET() macros were
> added
> > - * in glibc 2.3.3.
> > - *
> > - * CPU_COUNT() first appeared in glibc 2.6.
> > - *
> > - * CPU_AND(),     CPU_OR(),     CPU_XOR(),    CPU_EQUAL(),
> CPU_ALLOC(),
> > - * CPU_ALLOC_SIZE(), CPU_FREE(), CPU_ZERO_S(),  CPU_SET_S(),
> CPU_CLR_S(),
> > - * CPU_ISSET_S(),  CPU_AND_S(), CPU_OR_S(), CPU_XOR_S(), and
> CPU_EQUAL_S()
> > - * first appeared in glibc 2.7.
> > - */
> > -#if defined(CPU_ALLOC)
> > -	size_t size;
> > -	cpu_set_t *cpusetp;
> > -
> > -	cpusetp = CPU_ALLOC(RTE_MAX_LCORE);
> > -	if (cpusetp == NULL) {
> > -		RTE_LOG(ERR, EAL, "CPU_ALLOC failed\n");
> > -		return -1;
> > -	}
> > -
> > -	size = CPU_ALLOC_SIZE(RTE_MAX_LCORE);
> > -	CPU_ZERO_S(size, cpusetp);
> > -	CPU_SET_S(rte_lcore_id(), size, cpusetp);
> > +	unsigned lcore_id = rte_lcore_id();
> >
> >  	thread = pthread_self();
> > -	s = pthread_setaffinity_np(thread, size, cpusetp);
> > +	s = pthread_setaffinity_np(thread, sizeof(cpuset_t),
> > +				   &lcore_config[lcore_id].cpuset);
> >  	if (s != 0) {
> >  		RTE_LOG(ERR, EAL, "pthread_setaffinity_np failed\n");
> > -		CPU_FREE(cpusetp);
> >  		return -1;
> >  	}
> >
> > -	CPU_FREE(cpusetp);
> > -#else /* CPU_ALLOC */
> > -	cpuset_t cpuset;
> > -	CPU_ZERO( &cpuset );
> > -	CPU_SET( rte_lcore_id(), &cpuset );
> > +	/* acquire system unique id  */
> > +	rte_gettid();
> 
> As suggested in the previous patch, I think having rte_init_tid() would
> be clearer here.
[LCM] Sorry, I didn't get your [PATCH v4 07/17] comments, probably the mailbox issue.
Do you suggest to have a rte_init_tid() but not do syscall on the first time ?
Any benefit, rte_gettid() looks like more simple and straight forward. 
> > +
> > +	/* store socket_id in TLS for quick access */
> > +	RTE_PER_LCORE(_socket_id) =
> > +		eal_cpuset_socket_id(&lcore_config[lcore_id].cpuset);
> > +
> > +	CPU_COPY(&lcore_config[lcore_id].cpuset, &RTE_PER_LCORE(_cpuset));
> > +
> > +	lcore_config[lcore_id].socket_id = RTE_PER_LCORE(_socket_id);
> >
> > -	thread = pthread_self();
> > -	s = pthread_setaffinity_np(thread, sizeof( cpuset ), &cpuset);
> > -	if (s != 0) {
> > -		RTE_LOG(ERR, EAL, "pthread_setaffinity_np failed\n");
> > -		return -1;
> > -	}
> > -#endif
> 
> You are removing a lot of code that was using CPU_ALLOC().
> Are we sure that the cpuset_t type is large enough to store all the
> CPUs?
> 
> It looks the current value of CPU_SETSIZE is 1024 now, but I wonder
> if this code was written when this value was lower. Could you check if
> it can happen today (maybe with an old libc)? A problem can occur if
> the size of cpuset_t is lower that the size of RTE_MAX_LCORE.
[LCM] I found actually the MACRO is not just for support CPU_ALLOC(), but for linux or freebsd.
In freebsdapp, there's no CPU_ALLOC defined, it use fixed width *cpuset_t*.
In linuxapp, there's CPU_ALLOC defined, it use cpu_set_t* and dynamic CPU_ALLOC(RTE_MAX_LCORE).
But actually RTE_MAX_LCORE < 1024(sizeof(cpu_set_t)). 
After using rte_cpuset_t, there's no additional reason to use CPU_ALLOC only for linuxapp and choose a small but dynamic width.
> 
> 
> Regards,
> Olivier