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

Tony Lu
2022-11-23T11:26:06Z

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.
> >
> > >
> > > 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;
> > > 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.

Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>

Cheers,
Tony Lu

>
> - Jan
> >
> > Cheers,
> > Tony Lu
> >
> > > return 0;
> > > --
> > > 2.34.1