* [PATCH net] tun: remove possible false sharing in tun_flow_update()
@ 2019-10-09 16:20 Eric Dumazet
2019-10-10 3:59 ` Jason Wang
2019-10-10 4:29 ` Jakub Kicinski
0 siblings, 2 replies; 3+ messages in thread
From: Eric Dumazet @ 2019-10-09 16:20 UTC (permalink / raw)
To: David S . Miller
Cc: netdev, Eric Dumazet, Eric Dumazet, Jakub Kicinski, Zhang Yu,
Wang Li, Li RongQing, Jason Wang
As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance
a C compiler can legally transform
if (e->queue_index != queue_index)
e->queue_index = queue_index;
to :
e->queue_index = queue_index;
Note that the code using jiffies has no issue, since jiffies
has volatile attribute.
if (e->updated != jiffies)
e->updated = jiffies;
Fixes: 83b1bc122cab ("tun: align write-heavy flow entry members to a cache line")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Zhang Yu <zhangyu31@baidu.com>
Cc: Wang Li <wangli39@baidu.com>
Cc: Li RongQing <lirongqing@baidu.com>
Cc: Jason Wang <jasowang@redhat.com>
---
drivers/net/tun.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 812dc3a65efbb9d1ee2724e73978dbc4803ec171..a8d3141582a53caf407dc9aff61c452998de068f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -526,8 +526,8 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
e = tun_flow_find(head, rxhash);
if (likely(e)) {
/* TODO: keep queueing to old queue until it's empty? */
- if (e->queue_index != queue_index)
- e->queue_index = queue_index;
+ if (READ_ONCE(e->queue_index) != queue_index)
+ WRITE_ONCE(e->queue_index, queue_index);
if (e->updated != jiffies)
e->updated = jiffies;
sock_rps_record_flow_hash(e->rps_rxhash);
--
2.23.0.581.g78d2f28ef7-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net] tun: remove possible false sharing in tun_flow_update()
2019-10-09 16:20 [PATCH net] tun: remove possible false sharing in tun_flow_update() Eric Dumazet
@ 2019-10-10 3:59 ` Jason Wang
2019-10-10 4:29 ` Jakub Kicinski
1 sibling, 0 replies; 3+ messages in thread
From: Jason Wang @ 2019-10-10 3:59 UTC (permalink / raw)
To: Eric Dumazet, David S . Miller
Cc: netdev, Eric Dumazet, Jakub Kicinski, Zhang Yu, Wang Li, Li RongQing
On 2019/10/10 上午12:20, Eric Dumazet wrote:
> As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance
> a C compiler can legally transform
>
> if (e->queue_index != queue_index)
> e->queue_index = queue_index;
>
> to :
>
> e->queue_index = queue_index;
>
> Note that the code using jiffies has no issue, since jiffies
> has volatile attribute.
>
> if (e->updated != jiffies)
> e->updated = jiffies;
>
> Fixes: 83b1bc122cab ("tun: align write-heavy flow entry members to a cache line")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Zhang Yu <zhangyu31@baidu.com>
> Cc: Wang Li <wangli39@baidu.com>
> Cc: Li RongQing <lirongqing@baidu.com>
> Cc: Jason Wang <jasowang@redhat.com>
> ---
> drivers/net/tun.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 812dc3a65efbb9d1ee2724e73978dbc4803ec171..a8d3141582a53caf407dc9aff61c452998de068f 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -526,8 +526,8 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
> e = tun_flow_find(head, rxhash);
> if (likely(e)) {
> /* TODO: keep queueing to old queue until it's empty? */
> - if (e->queue_index != queue_index)
> - e->queue_index = queue_index;
> + if (READ_ONCE(e->queue_index) != queue_index)
> + WRITE_ONCE(e->queue_index, queue_index);
> if (e->updated != jiffies)
> e->updated = jiffies;
> sock_rps_record_flow_hash(e->rps_rxhash);
Acked-by: Jason Wang <jasowang@redhat.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net] tun: remove possible false sharing in tun_flow_update()
2019-10-09 16:20 [PATCH net] tun: remove possible false sharing in tun_flow_update() Eric Dumazet
2019-10-10 3:59 ` Jason Wang
@ 2019-10-10 4:29 ` Jakub Kicinski
1 sibling, 0 replies; 3+ messages in thread
From: Jakub Kicinski @ 2019-10-10 4:29 UTC (permalink / raw)
To: Eric Dumazet
Cc: David S . Miller, netdev, Eric Dumazet, Zhang Yu, Wang Li,
Li RongQing, Jason Wang
On Wed, 9 Oct 2019 09:20:02 -0700, Eric Dumazet wrote:
> As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance
> a C compiler can legally transform
>
> if (e->queue_index != queue_index)
> e->queue_index = queue_index;
>
> to :
>
> e->queue_index = queue_index;
>
> Note that the code using jiffies has no issue, since jiffies
> has volatile attribute.
>
> if (e->updated != jiffies)
> e->updated = jiffies;
>
> Fixes: 83b1bc122cab ("tun: align write-heavy flow entry members to a cache line")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Zhang Yu <zhangyu31@baidu.com>
> Cc: Wang Li <wangli39@baidu.com>
> Cc: Li RongQing <lirongqing@baidu.com>
> Cc: Jason Wang <jasowang@redhat.com>
Applied, same story with stable, thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-10-10 4:29 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-09 16:20 [PATCH net] tun: remove possible false sharing in tun_flow_update() Eric Dumazet
2019-10-10 3:59 ` Jason Wang
2019-10-10 4:29 ` Jakub Kicinski
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).