netdev - [PATCH net-next] net/smc: increase SMC_WR_BUF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241025074619.59864-1-wenjia@linux.ibm.com>
Date: Fri, 25 Oct 2024 09:46:19 +0200
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: Wen Gu <guwen@...ux.alibaba.com>, "D. Wythe" <alibuda@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>, David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>, Jan Karcher <jaka@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>, Nils Hoppmann <niho@...ux.ibm.com>,
        Niklas Schnell <schnelle@...ux.ibm.com>,
        Thorsten Winkler <twinkler@...ux.ibm.com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Stefan Raspl <raspl@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>
Subject: [PATCH net-next] net/smc: increase SMC_WR_BUF_CNT

From: Halil Pasic <pasic@...ux.ibm.com>

The current value of SMC_WR_BUF_CNT is 16 which leads to heavy
contention on the wr_tx_wait workqueue of the SMC-R linkgroup and its
spinlock when many connections are  competing for the buffer. Currently
up to 256 connections per linkgroup are supported.

To make things worse when finally a buffer becomes available and
smc_wr_tx_put_slot() signals the linkgroup's wr_tx_wait wq, because
WQ_FLAG_EXCLUSIVE is not used all the waiters get woken up, most of the
time a single one can proceed, and the rest is contending on the
spinlock of the wq to go to sleep again.

For some reason include/linux/wait.h does not offer a top level wrapper
macro for wait_event with interruptible, exclusive and timeout. I did
not spend too many cycles on thinking if that is even a combination that
makes sense (on the quick I don't see why not) and conversely I
refrained from making an attempt to accomplish the interruptible,
exclusive and timeout combo by using the abstraction-wise lower
level __wait_event interface.

To alleviate the tx performance bottleneck and the CPU overhead due to
the spinlock contention, let us increase SMC_WR_BUF_CNT to 256.

Signed-off-by: Halil Pasic <pasic@...ux.ibm.com>
Reported-by: Nils Hoppmann <niho@...ux.ibm.com>
Reviewed-by: Wenjia Zhang <wenjia@...ux.ibm.com>
Signed-off-by: Wenjia Zhang <wenjia@...ux.ibm.com>
---
 net/smc/smc_wr.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/smc/smc_wr.h b/net/smc/smc_wr.h
index f3008dda222a..81e772e241f3 100644
--- a/net/smc/smc_wr.h
+++ b/net/smc/smc_wr.h
@@ -19,7 +19,7 @@
 #include "smc.h"
 #include "smc_core.h"

-#define SMC_WR_BUF_CNT 16	/* # of ctrl buffers per link */
+#define SMC_WR_BUF_CNT 256	/* # of ctrl buffers per link */

 #define SMC_WR_TX_WAIT_FREE_SLOT_TIME	(10 * HZ)

-- 
2.43.0