Re: [PATCH net-next] net/smc: Unbind smc control from tcp control

Alexandra Winter
2022-11-24T13:01:19Z

On 23.11.22 12:25, Tony Lu wrote:
> On Wed, Nov 23, 2022 at 12:19:19PM +0100, Jan Karcher wrote:
>>
>>
>> On 23/11/2022 12:13, Tony Lu wrote:
>>> On Wed, Nov 23, 2022 at 11:58:30AM +0100, Jan Karcher wrote:
>>>> In the past SMC used the values of tcp_{w|r}mem to create the send
>>>> buffer and RMB. We now have our own sysctl knobs to tune them without
>>>> influencing the TCP default.
>>>>
>>>> This patch removes the dependency on the TCP control by providing our
>>>> own initial values which aim for a low memory footprint.
>>>
>>> +1, before introducing sysctl knobs of SMC, we were going to get rid of
>>> TCP and have SMC own values. Now this does it, So I very much agree with
>>> this.
>>>
Iiuc you are changing the default values in this a patch and your other patch:
Default values for real_buf for send and receive:

before 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable")
real_buf=net.ipv4.tcp_{w|r}mem[1]/2 send: 8k recv: 64k

after 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable")
real_buf=net.ipv4.tcp_{w|r}mem[1] send: 16k (16*1024) recv: 128k (131072)

after net/smc: Fix expected buffersizes and sync logic
real_buf=net.ipv4.tcp_{w|r}mem[1] send: 16k (16*1024) recv: 128k (131072)

after net/smc: Unbind smc control from tcp control
real_buf=SMC_*BUF_INIT_SIZE send: 16k (16384) recv: 64k (65536)

If my understanding is correct, then I nack this.
Defaults should be restored to the values before 0227f058aa29.
Otherwise users will notice a change in memory usage that needs to
be avoided or announced more explicitely. (and don't change them twice)

>>>>
>>>> Signed-off-by: Jan Karcher <jaka@linux.ibm.com>
>>>> Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
>>>> ---
>>>> Documentation/networking/smc-sysctl.rst | 4 ++--
>>>> net/smc/smc_core.h | 6 ++++--
>>>> net/smc/smc_sysctl.c | 10 ++++++----
>>>> 3 files changed, 12 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/Documentation/networking/smc-sysctl.rst b/Documentation/networking/smc-sysctl.rst
>>>> index 6d8acdbe9be1..a1c634d3690a 100644
>>>> --- a/Documentation/networking/smc-sysctl.rst
>>>> +++ b/Documentation/networking/smc-sysctl.rst
>>>> @@ -44,7 +44,7 @@ smcr_testlink_time - INTEGER
>>>> wmem - INTEGER
>>>> Initial size of send buffer used by SMC sockets.
>>>> - The default value inherits from net.ipv4.tcp_wmem[1].
>>>> + The default value aims for a small memory footprint and is set to 16KiB.
>>>> The minimum value is 16KiB and there is no hard limit for max value, but
>>>> only allowed 512KiB for SMC-R and 1MiB for SMC-D.
>>>> @@ -53,7 +53,7 @@ wmem - INTEGER
>>>> rmem - INTEGER
>>>> Initial size of receive buffer (RMB) used by SMC sockets.
>>>> - The default value inherits from net.ipv4.tcp_rmem[1].
>>>> + The default value aims for a small memory footprint and is set to 64KiB.
>>>> The minimum value is 16KiB and there is no hard limit for max value, but
>>>> only allowed 512KiB for SMC-R and 1MiB for SMC-D.
>>>> diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
>>>> index 285f9bd8e232..67c3937f341d 100644
>>>> --- a/net/smc/smc_core.h
>>>> +++ b/net/smc/smc_core.h
>>>> @@ -206,8 +206,10 @@ struct smc_rtoken { /* address/key of remote RMB */
>>>> u32 rkey;
>>>> };
>>>> -#define SMC_BUF_MIN_SIZE 16384 /* minimum size of an RMB */
>>>> -#define SMC_RMBE_SIZES 16 /* number of distinct RMBE sizes */
>>>> +#define SMC_SNDBUF_INIT_SIZE 16384 /* initial size of send buffer */
>>>> +#define SMC_RCVBUF_INIT_SIZE 65536 /* initial size of receive buffer */
>>>> +#define SMC_BUF_MIN_SIZE 16384 /* minimum size of an RMB */
>>>> +#define SMC_RMBE_SIZES 16 /* number of distinct RMBE sizes */
>>>> /* theoretically, the RFC states that largest size would be 512K,
>>>> * i.e. compressed 5 and thus 6 sizes (0..5), despite
>>>> * struct smc_clc_msg_accept_confirm.rmbe_size being a 4 bit value (0..15)
>>>> diff --git a/net/smc/smc_sysctl.c b/net/smc/smc_sysctl.c
>>>> index b6f79fabb9d3..a63aa79d4856 100644
>>>> --- a/net/smc/smc_sysctl.c
>>>> +++ b/net/smc/smc_sysctl.c
>>>> @@ -19,8 +19,10 @@
>>>> #include "smc_llc.h"
>>>> #include "smc_sysctl.h"
>>>> -static int min_sndbuf = SMC_BUF_MIN_SIZE;
>>>> -static int min_rcvbuf = SMC_BUF_MIN_SIZE;
>>>> +static int initial_sndbuf = SMC_SNDBUF_INIT_SIZE;
>>>> +static int initial_rcvbuf = SMC_RCVBUF_INIT_SIZE;
>>>> +static int min_sndbuf = SMC_BUF_MIN_SIZE;
>>>> +static int min_rcvbuf = SMC_BUF_MIN_SIZE;
Broken formatting
>>>> static struct ctl_table smc_table[] = {
>>>> {
>>>> @@ -88,8 +90,8 @@ int __net_init smc_sysctl_net_init(struct net *net)
>>>> net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
>>>> net->smc.sysctl_smcr_buf_type = SMCR_PHYS_CONT_BUFS;
>>>> net->smc.sysctl_smcr_testlink_time = SMC_LLC_TESTLINK_DEFAULT_TIME;
>>>> - WRITE_ONCE(net->smc.sysctl_wmem, READ_ONCE(net->ipv4.sysctl_tcp_wmem[1]));
>>>> - WRITE_ONCE(net->smc.sysctl_rmem, READ_ONCE(net->ipv4.sysctl_tcp_rmem[1]));
>>>> + WRITE_ONCE(net->smc.sysctl_wmem, initial_sndbuf);
>>>> + WRITE_ONCE(net->smc.sysctl_rmem, initial_rcvbuf);
>>>
>>> Maybe we can use SMC_{SND|RCV}BUF_INIT_SIZE macro directly, instead of
>>> new variables.
>>
>> The reason i created the new variables is that min_{snd|rcv}buf also have
>> their own variables. I know it is not needed but thought it was cleaner.
>> If you have a strong opinion on using the value directly i can change it.
>> Please let me know if you want it changed.
>
> Yep, it's okay for me to use variables or macros. Just let it be.
I think it's better coding style to use the macros instead of unneccessary variables.
At least the variables could be defined as const.
>
> Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
>
> Cheers,
> Tony Lu
>
>>
>> - Jan
>>>
>>> Cheers,
>>> Tony Lu
>>>
>>>> return 0;
>>>> --
>>>> 2.34.1