RE: [PATCH] lib/mempool : rte_mempool_avail_count, fixing return bigger than mempool size

[Morten Brørup]

From: Yasin CANER [mailto:yasinnca...@gmail.com] 
Sent: Wednesday, 17 May 2023 10.01
To: Morten Brørup
Cc: Stephen Hemminger; dev@dpdk.org; Yasin CANER; Olivier Matz; Andrew Rybchenko
Subject: Re: [PATCH] lib/mempool : rte_mempool_avail_count, fixing return 
bigger than mempool size

 

Hello,

 

I don't have full knowledge of how to work rte_mempool_ops_get_count() but 
there is another comment about it. Maybe it relates. 

/*
 * due to race condition (access to len is not locked), the
 * total can be greater than size... so fix the result
 */

 

MB: This comment relates to the race when accessing the per-lcore cache 
counters.

 

Best regards.

 

Morten Brørup <m...@smartsharesystems.com>, 16 May 2023 Sal, 19:04 tarihinde 
şunu yazdı:

        > From: Stephen Hemminger [mailto:step...@networkplumber.org]
        > Sent: Tuesday, 16 May 2023 17.24
        > 
        > On Tue, 16 May 2023 13:41:46 +0000
        > Yasin CANER <yasinnca...@gmail.com> wrote:
        > 
        > > From: Yasin CANER <yasin.ca...@ulakhaberlesme.com.tr>
        > >
        > > after a while working rte_mempool_avail_count function returns 
bigger
        > > than mempool size that cause miscalculation 
rte_mempool_in_use_count.
        > >
        > > it helps to avoid miscalculation rte_mempool_in_use_count.
        > >
        > > Bugzilla ID: 1229
        > >
        > > Signed-off-by: Yasin CANER <yasin.ca...@ulakhaberlesme.com.tr>
        > 
        > An alternative that avoids some code duplication.
        > 
        > diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
        > index cf5dea2304a7..2406b112e7b0 100644
        > --- a/lib/mempool/rte_mempool.c
        > +++ b/lib/mempool/rte_mempool.c
        > @@ -1010,7 +1010,7 @@ rte_mempool_avail_count(const struct rte_mempool
        > *mp)
        >         count = rte_mempool_ops_get_count(mp);
        > 
        >         if (mp->cache_size == 0)
        > -               return count;
        > +               goto exit;
        
        This bug can only occur here (i.e. with cache_size==0) if 
rte_mempool_ops_get_count() returns an incorrect value. The bug should be fixed 
there instead.
        
        > 
        >         for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++)
        >                 count += mp->local_cache[lcore_id].len;
        > @@ -1019,6 +1019,7 @@ rte_mempool_avail_count(const struct rte_mempool
        > *mp)
        >          * due to race condition (access to len is not locked), the
        >          * total can be greater than size... so fix the result
        >          */
        > +exit:
        >         if (count > mp->size)
        >                 return mp->size;
        >         return count;