Re: [PATCH] net/smc: avoid atomic_set and smp_wmb in the tx path when possible
From: Wenjia Zhang <hidden>
Date: 2023-11-02 20:42:39
Also in:
linux-s390
On 02.11.23 10:27, Li RongQing wrote:
these is less opportunity that conn->tx_pushing is not 1, since tx_pushing is just checked with 1, so move the setting tx_pushing to 1 after atomic_dec_and_test() return false, to avoid atomic_set and smp_wmb in tx path when possible
I think we should avoid to use argument like "less opportunity" in commit message. Because "less opportunity" does not mean "no opportunity". Once it occurs, does it mean that what the patch changes is useless or wrong?
quoted hunk ↗ jump to hunk
Signed-off-by: Li RongQing <redacted> --- net/smc/smc_tx.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c index 3b0ff3b..72dbdee 100644 --- a/net/smc/smc_tx.c +++ b/net/smc/smc_tx.c@@ -667,8 +667,6 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn) return 0; again: - atomic_set(&conn->tx_pushing, 1); - smp_wmb(); /* Make sure tx_pushing is 1 before real send */ rc = __smc_tx_sndbuf_nonempty(conn); /* We need to check whether someone else have added some data into@@ -677,8 +675,11 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn) * If so, we need to push again to prevent those data hang in the send * queue. */ - if (unlikely(!atomic_dec_and_test(&conn->tx_pushing))) + if (unlikely(!atomic_dec_and_test(&conn->tx_pushing))) { + atomic_set(&conn->tx_pushing, 1); + smp_wmb(); /* Make sure tx_pushing is 1 before real send */ goto again; + } return rc; }
I'm afraid that the *if* statement would never be true, without setting the value of &conn->tx_pushing firstly.