diff mbox series

[v4,2/4] ring: read tail using atomic load

Message ID 1537171879-64390-2-git-send-email-gavin.hu@arm.com (mailing list archive)
State Superseded, archived
Headers
Series [v4,1/4] bus/fslmc: fix undefined reference of memsegs |

Checks

Context Check Description
ci/checkpatch success coding style OK
ci/Intel-compilation success Compilation OK

Commit Message

Gavin Hu Sept. 17, 2018, 8:11 a.m. UTC 
  In update_tail, read ht->tail using __atomic_load.Although the
compiler currently seems to be doing the right thing even without
_atomic_load, we don't want to give the compiler freedom to optimise
what should be an atomic load, it should not be arbitarily moved
around.

Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option")
Cc: stable@dpdk.org

Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
---
 lib/librte_ring/rte_ring_c11_mem.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Jerin Jacob Sept. 20, 2018, 6:41 a.m. UTC | #1 
-----Original Message-----
> Date: Mon, 17 Sep 2018 16:11:17 +0800
> From: Gavin Hu <gavin.hu@arm.com>
> To: dev@dpdk.org
> CC: gavin.hu@arm.com, Honnappa.Nagarahalli@arm.com, steve.capper@arm.com,
>  Ola.Liljedahl@arm.com, jerin.jacob@caviumnetworks.com, nd@arm.com,
>  stable@dpdk.org
> Subject: [PATCH v4 2/4] ring: read tail using atomic load
> X-Mailer: git-send-email 2.7.4
> 
> 
> In update_tail, read ht->tail using __atomic_load.Although the
> compiler currently seems to be doing the right thing even without
> _atomic_load, we don't want to give the compiler freedom to optimise
> what should be an atomic load, it should not be arbitarily moved
> around.
> 
> Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option")
> Cc: stable@dpdk.org


+ Jia He <jia.he@hxt-semitech.com>

> 
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Reviewed-by: Steve Capper <steve.capper@arm.com>
> Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
> ---
>  lib/librte_ring/rte_ring_c11_mem.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h
> index 94df3c4..234fea0 100644
> --- a/lib/librte_ring/rte_ring_c11_mem.h
> +++ b/lib/librte_ring/rte_ring_c11_mem.h
> @@ -21,7 +21,8 @@ update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
>          * we need to wait for them to complete
>          */
>         if (!single)
> -               while (unlikely(ht->tail != old_val))
> +               while (unlikely(old_val != __atomic_load_n(&ht->tail,
> +                                               __ATOMIC_RELAXED)))
>                         rte_pause();
> 
>         __atomic_store_n(&ht->tail, new_val, __ATOMIC_RELEASE);
> --
> 2.7.4
>
Gavin Hu Sept. 25, 2018, 9:26 a.m. UTC | #2 
+ Justin He as Jerin requested. 

> -----Original Message-----
> From: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> Sent: Thursday, September 20, 2018 2:41 PM
> To: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>
> Cc: dev@dpdk.org; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Steve Capper
> <Steve.Capper@arm.com>; Ola Liljedahl <Ola.Liljedahl@arm.com>; nd
> <nd@arm.com>; stable@dpdk.org; jia.he@hxt-semitech.com
> Subject: Re: [PATCH v4 2/4] ring: read tail using atomic load
> 
> -----Original Message-----
> > Date: Mon, 17 Sep 2018 16:11:17 +0800
> > From: Gavin Hu <gavin.hu@arm.com>
> > To: dev@dpdk.org
> > CC: gavin.hu@arm.com, Honnappa.Nagarahalli@arm.com,
> > steve.capper@arm.com,  Ola.Liljedahl@arm.com,
> > jerin.jacob@caviumnetworks.com, nd@arm.com,  stable@dpdk.org
> > Subject: [PATCH v4 2/4] ring: read tail using atomic load
> > X-Mailer: git-send-email 2.7.4
> >
> >
> > In update_tail, read ht->tail using __atomic_load.Although the
> > compiler currently seems to be doing the right thing even without
> > _atomic_load, we don't want to give the compiler freedom to optimise
> > what should be an atomic load, it should not be arbitarily moved
> > around.
> >
> > Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option")
> > Cc: stable@dpdk.org
> 
> 
> + Jia He <jia.he@hxt-semitech.com>
> 
> >
> > Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> > Reviewed-by: Steve Capper <steve.capper@arm.com>
> > Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
> > ---
> >  lib/librte_ring/rte_ring_c11_mem.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_ring/rte_ring_c11_mem.h
> > b/lib/librte_ring/rte_ring_c11_mem.h
> > index 94df3c4..234fea0 100644
> > --- a/lib/librte_ring/rte_ring_c11_mem.h
> > +++ b/lib/librte_ring/rte_ring_c11_mem.h
> > @@ -21,7 +21,8 @@ update_tail(struct rte_ring_headtail *ht, uint32_t
> old_val, uint32_t new_val,
> >          * we need to wait for them to complete
> >          */
> >         if (!single)
> > -               while (unlikely(ht->tail != old_val))
> > +               while (unlikely(old_val != __atomic_load_n(&ht->tail,
> > +                                               __ATOMIC_RELAXED)))
> >                         rte_pause();
> >
> >         __atomic_store_n(&ht->tail, new_val, __ATOMIC_RELEASE);
> > --
> > 2.7.4
> >
diff mbox series

Patch

diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h
index 94df3c4..234fea0 100644
--- a/lib/librte_ring/rte_ring_c11_mem.h
+++ b/lib/librte_ring/rte_ring_c11_mem.h
@@ -21,7 +21,8 @@  update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
 	 * we need to wait for them to complete
 	 */
 	if (!single)
-		while (unlikely(ht->tail != old_val))
+		while (unlikely(old_val != __atomic_load_n(&ht->tail,
+						__ATOMIC_RELAXED)))
 			rte_pause();
 
 	__atomic_store_n(&ht->tail, new_val, __ATOMIC_RELEASE);