[PATCH net-next v2 0/2] net/smc: Change the upper boundary of SMC-R's snd_buf and rcv_buf to 512MB

[PATCH net-next v2 0/2] net/smc: Change the upper boundary of SMC-R's snd_buf and rcv_buf to 512MB

[Guangguan Wang]

SMCR_RMBE_SIZES is the upper boundary of SMC-R's snd_buf and rcv_buf.
The maximum bytes of snd_buf and rcv_buf can be calculated by 2^SMCR_
RMBE_SIZES * 16KB. SMCR_RMBE_SIZES = 5 means the upper boundary is 512KB.
TCP's snd_buf and rcv_buf max size is configured by net.ipv4.tcp_w/rmem[2]
whose default value is 4MB or 6MB, is much larger than SMC-R's upper
boundary.

In some scenarios, such as Recommendation System, the communication
pattern is mainly large size send/recv, where the size of snd_buf and
rcv_buf greatly affects performance. Due to the upper boundary
disadvantage, SMC-R performs poor than TCP in those scenarios. So it
is time to enlarge the upper boundary size of SMC-R's snd_buf and rcv_buf,
so that the SMC-R's snd_buf and rcv_buf can be configured to larger size
for performance gain in such scenarios.

The SMC-R rcv_buf's size will be transferred to peer by the field
rmbe_size in clc accept and confirm message. The length of the field
rmbe_size is four bits, which means the maximum value of SMCR_RMBE_SIZES
is 15. In case of frequently adjusting the value of SMCR_RMBE_SIZES
in different scenarios, set the value of SMCR_RMBE_SIZES to the maximum
value 15, which means the upper boundary of SMC-R's snd_buf and rcv_buf
is 512MB. As the real memory usage is determined by the value of
net.smc.w/rmem, not by the upper boundary, set the value of SMCR_RMBE_SIZES
to the maximum value has no side affects.

Guangguan Wang (2):
  net/smc: set rmb's SG_MAX_SINGLE_ALLOC limitation only when
    CONFIG_ARCH_NO_SG_CHAIN is defined
  net/smc: change SMCR_RMBE_SIZES from 5 to 15

 net/smc/smc_core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

-- 
2.24.3 (Apple Git-128)

[PATCH net-next v2 1/2] net/smc: set rmb's SG_MAX_SINGLE_ALLOC limitation only when CONFIG_ARCH_NO_SG_CHAIN is defined

[Guangguan Wang]

SG_MAX_SINGLE_ALLOC is used to limit maximum number of entries that
will be allocated in one piece of scatterlist. When the entries of
scatterlist exceeds SG_MAX_SINGLE_ALLOC, sg chain will be used. From
commit 7c703e54cc71 ("arch: switch the default on ARCH_HAS_SG_CHAIN"),
we can know that the macro CONFIG_ARCH_NO_SG_CHAIN is used to identify
whether sg chain is supported. So, SMC-R's rmb buffer should be limited
by SG_MAX_SINGLE_ALLOC only when the macro CONFIG_ARCH_NO_SG_CHAIN is
defined.

Fixes: a3fe3d01bd0d ("net/smc: introduce sg-logic for RMBs")
Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
Co-developed-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
---
 net/smc/smc_core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index fafdb97adfad..acca3b1a068f 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -2015,7 +2015,6 @@ int smc_conn_create(struct smc_sock *smc, struct smc_init_info *ini)
  */
 static u8 smc_compress_bufsize(int size, bool is_smcd, bool is_rmb)
 {
-	const unsigned int max_scat = SG_MAX_SINGLE_ALLOC * PAGE_SIZE;
 	u8 compressed;
 
 	if (size <= SMC_BUF_MIN_SIZE)
@@ -2025,9 +2024,11 @@ static u8 smc_compress_bufsize(int size, bool is_smcd, bool is_rmb)
 	compressed = min_t(u8, ilog2(size) + 1,
 			   is_smcd ? SMCD_DMBE_SIZES : SMCR_RMBE_SIZES);
 
+#ifdef CONFIG_ARCH_NO_SG_CHAIN
 	if (!is_smcd && is_rmb)
 		/* RMBs are backed by & limited to max size of scatterlists */
-		compressed = min_t(u8, compressed, ilog2(max_scat >> 14));
+		compressed = min_t(u8, compressed, ilog2((SG_MAX_SINGLE_ALLOC * PAGE_SIZE) >> 14));
+#endif
 
 	return compressed;
 }
-- 
2.24.3 (Apple Git-128)

[PATCH net-next v2 2/2] net/smc: change SMCR_RMBE_SIZES from 5 to 15

[Guangguan Wang]

SMCR_RMBE_SIZES is the upper boundary of SMC-R's snd_buf and rcv_buf.
The maximum bytes of snd_buf and rcv_buf can be calculated by 2^SMCR_
RMBE_SIZES * 16KB. SMCR_RMBE_SIZES = 5 means the upper boundary is 512KB.
TCP's snd_buf and rcv_buf max size is configured by net.ipv4.tcp_w/rmem[2]
whose default value is 4MB or 6MB, is much larger than SMC-R's upper
boundary.

In some scenarios, such as Recommendation System, the communication
pattern is mainly large size send/recv, where the size of snd_buf and
rcv_buf greatly affects performance. Due to the upper boundary
disadvantage, SMC-R performs poor than TCP in those scenarios. So it
is time to enlarge the upper boundary size of SMC-R's snd_buf and rcv_buf,
so that the SMC-R's snd_buf and rcv_buf can be configured to larger size
for performance gain in such scenarios.

The SMC-R rcv_buf's size will be transferred to peer by the field
rmbe_size in clc accept and confirm message. The length of the field
rmbe_size is four bits, which means the maximum value of SMCR_RMBE_SIZES
is 15. In case of frequently adjusting the value of SMCR_RMBE_SIZES
in different scenarios, set the value of SMCR_RMBE_SIZES to the maximum
value 15, which means the upper boundary of SMC-R's snd_buf and rcv_buf
is 512MB. As the real memory usage is determined by the value of
net.smc.w/rmem, not by the upper boundary, set the value of SMCR_RMBE_SIZES
to the maximum value has no side affects.

Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
Co-developed-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
---
 net/smc/smc_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index acca3b1a068f..3b95828d9976 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -2006,7 +2006,7 @@ int smc_conn_create(struct smc_sock *smc, struct smc_init_info *ini)
 }
 
 #define SMCD_DMBE_SIZES		6 /* 0 -> 16KB, 1 -> 32KB, .. 6 -> 1MB */
-#define SMCR_RMBE_SIZES		5 /* 0 -> 16KB, 1 -> 32KB, .. 5 -> 512KB */
+#define SMCR_RMBE_SIZES		15 /* 0 -> 16KB, 1 -> 32KB, .. 15 -> 512MB */
 
 /* convert the RMB size into the compressed notation (minimum 16K, see
  * SMCD/R_DMBE_SIZES.
-- 
2.24.3 (Apple Git-128)

Re: [PATCH net-next v2 0/2] net/smc: Change the upper boundary of SMC-R's snd_buf and rcv_buf to 512MB

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by David S. Miller <davem@davemloft.net>:

On Mon,  3 Jun 2024 11:00:17 +0800 you wrote:
> SMCR_RMBE_SIZES is the upper boundary of SMC-R's snd_buf and rcv_buf.
> The maximum bytes of snd_buf and rcv_buf can be calculated by 2^SMCR_
> RMBE_SIZES * 16KB. SMCR_RMBE_SIZES = 5 means the upper boundary is 512KB.
> TCP's snd_buf and rcv_buf max size is configured by net.ipv4.tcp_w/rmem[2]
> whose default value is 4MB or 6MB, is much larger than SMC-R's upper
> boundary.
> 
> [...]

Here is the summary with links:
  - [net-next,v2,1/2] net/smc: set rmb's SG_MAX_SINGLE_ALLOC limitation only when CONFIG_ARCH_NO_SG_CHAIN is defined
    https://git.kernel.org/netdev/net-next/c/3ac14b9dfbd3
  - [net-next,v2,2/2] net/smc: change SMCR_RMBE_SIZES from 5 to 15
    https://git.kernel.org/netdev/net-next/c/2f4b101c542e

You are awesome, thank you!
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