[dpdk-dev] [PATCH v3] mempool: remove non-EAL thread note from header
Olivier Matz
olivier.matz at 6wind.com
Thu Mar 30 17:12:54 CEST 2017
Hi Gage,
On Wed, 29 Mar 2017 15:30:49 +0000, "Eads, Gage" <gage.eads at intel.com> wrote:
> > -----Original Message-----
> > From: Olivier Matz [mailto:olivier.matz at 6wind.com]
> > Sent: Friday, March 24, 2017 9:05 AM
> > To: Eads, Gage <gage.eads at intel.com>
> > Cc: dev at dpdk.org
> > Subject: Re: [PATCH v3] mempool: remove non-EAL thread note from header
> >
> > Hi Gage,
> >
> > On Thu, 23 Mar 2017 09:20:58 -0500, Gage Eads <gage.eads at intel.com>
> > wrote:
> > > Commit 30e6399892276 ("mempool: support non-EAL thread") added the
> > > capability for non-EAL threads to use the mempool library. This commit
> > > removes the note indicating that the mempool library cannot be used
> > > safely by non-EAL threads.
> > >
> > > Also, fix a typo.
> > >
> > > Signed-off-by: Gage Eads <gage.eads at intel.com>
> > > ---
> > > v2: Changed commit message to referenced commit 30e63998 instead of
> > > 4b5062755
> > > v3: Fix checkpatch error
> > >
> > > lib/librte_mempool/rte_mempool.h | 6 +-----
> > > 1 file changed, 1 insertion(+), 5 deletions(-)
> > >
> > > diff --git a/lib/librte_mempool/rte_mempool.h
> > > b/lib/librte_mempool/rte_mempool.h
> > > index 991feaa..b1186fd 100644
> > > --- a/lib/librte_mempool/rte_mempool.h
> > > +++ b/lib/librte_mempool/rte_mempool.h
> > > @@ -53,11 +53,7 @@
> > > *
> > > * Note: the mempool implementation is not preemptable. A lcore must
> > > * not be interrupted by another task that uses the same mempool
> > > - * (because it uses a ring which is not preemptable). Also, mempool
> > > - * functions must not be used outside the DPDK environment: for
> > > - * example, in linuxapp environment, a thread that is not created by
> > > - * the EAL must not use mempools. This is due to the per-lcore cache
> > > - * that won't work as rte_lcore_id() will not return a correct value.
> > > + * (because it uses a ring which is not preemptible).
> > > */
> > >
> > > #include <stdio.h>
> >
> > I agree the comment is not correct today. But I think we should still highlight
> > that usual functions [ex: rte_mempool_get(), rte_mempool_put()] won't work
> > when called on a non-EAL thread.
>
> My understanding is that non-EAL threads can call those functions, but their performance will suffer since they go directly to the underlying ring. Is that correct?
Yes, that's more correct than what I wrote :)
>
> >
> > Maybe it could be reworded in that way:
> >
> > """
> > Note: the mempool implementation is not preemptable. A lcore must not be
> > interrupted by another task that uses the same mempool (because it uses a ring
> > which is not preemptible). Also, usual mempool functions like
> > rte_mempool_get() or rte_mempool_put() are designed to be called from an
> > EAL thread due to the internal per-lcore cache. When using a mempool from a
> > non-EAL thread, a user cache has to be provided to
> > rte_mempool_generic_get() or rte_mempool_generic_put().
> > """
> >
> > What do you think?
>
> Agreed, this looks better. If indeed non-EAL threads can call rte_mempool_get() and _put(), perhaps the last sentence can be reworked like so?
>
> Due to the lack of caching, rte_mempool_get() or rte_mempool_put() performance
> will suffer when called by non-EAL threads. Instead, non-EAL threads should call
> rte_mempool_generic_get() or rte_mempool_generic_put() with a user cache
> created with rte_mempool_cache_create().
Looks good, thanks!
Olivier
>
> >
> > Thanks,
> > Olivier
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