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

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Date:   Wed, 23 Nov 2022 19:25:23 +0800
From:   Tony Lu <tonylu@...ux.alibaba.com>
To:     Jan Karcher <jaka@...ux.ibm.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Thorsten Winkler <twinkler@...ux.ibm.com>,
        Stefan Raspl <raspl@...ux.ibm.com>,
        Karsten Graul <kgraul@...ux.ibm.com>
Subject: Re: [PATCH net-next] net/smc: Unbind smc control from tcp control

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@...ux.ibm.com>
> > > Reviewed-by: Wenjia Zhang <wenjia@...ux.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@...ux.alibaba.com>

Cheers,
Tony Lu

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