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Message-ID: <Y4Q6IKPF4qw4EDBd@TonyMac-Alibaba> Date: Mon, 28 Nov 2022 12:33:36 +0800 From: Tony Lu <tonylu@...ux.alibaba.com> To: Alexandra Winter <wintera@...ux.ibm.com>, 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>, 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] net/smc: Fix expected buffersizes and sync logic On Fri, Nov 25, 2022 at 11:59:46AM +0100, Alexandra Winter wrote: > > > On 25.11.22 08:05, Tony Lu wrote: > > On Fri, Nov 25, 2022 at 07:15:33AM +0100, Jan Karcher wrote: > >> > >> > >> On 24/11/2022 15:07, Alexandra Winter wrote: > >>> > >>> > >>> On 24.11.22 14:00, Alexandra Winter wrote: > >>>> > >>>> > >> [ ... ]>>>>> On Wed, Nov 23, 2022 at 11:49:07AM +0100, Jan Karcher wrote: > >>>>>>>> The fixed commit changed the expected behavior of buffersizes > >>>>>>>> set by the user using the setsockopt mechanism. > >>>>>>>> Before the fixed patch the logic for determining the buffersizes used > >>>>>>>> was the following: > >>>>>>>> > >>>>>>>> default = net.ipv4.tcp_{w|r}mem[1] > >>> Jan, you explained to me: "the minima is 16Kib. This is enforced in smc_compress_bufsize > >>> which would move any value <= 16Kib into bucket 0 - which is 16KiB " > >>> net.ipv4.tcp_wmem[1] defaults to 8Kib. So in the default case (unchanged net.ipv4.tcp_wmem[1]) > >>> the default for the send path is not net.ipv4.tcp_wmem[1]. Should be clarified here. > >> > >> The default value is still set to the net.ipv4.tcp_{w|r}mem[1]. This is a > >> *very* top level overview about what is happening and *not* a documentation. > >> I don't really want to explain the full code flow here. > >> > >> What we still should do - as Tony aggreed on - is documenting the SMC > >> behavior. This is a follow up on my list. > > > > Hello Jan and Alexandra, > > > > It looks like the misalignment of information is causing some trouble, > > which is introduced by my patch. Maybe we could have an off-maillist and > > online meeting to discussion? > > > > We have some progress updates of scalability, and we are really like the > > extension of SMC-D. Also we have some ideas for SMC, in case of > > misalignment of information, we'd like to put them on the table and > > discuss them earlier. Maybe an online meeting is an efficient way. What > > do you think? > > > > If possible, I would prepared the meetings and topics and send them to > > everyone first. > > > > Cheers, > > Tony Lu > > > > Thanks a lot for your constructive proposals Tony. Yes, we should have a discussion off-mailinglist > about future topics. I will prepare the discussion off-maillinglist ASAP. The email will be sent out when it's ready. And Jan, What about your opinion? Cheers, Tony Lu > > My remaining concern for this fix is the default values (user does not use setsockopt, nor > changes the new sysfs parameters, nor changes tcp defaults): > >>>> before 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable") > send: 16k recv: 64k > >>>> after net/smc: Fix expected buffersizes and sync logic (this patch) > >>>> send: 16k recv: 128k > > @Jan, as this is the only patch you want to send to net, please change the default size of > the receive buffers back to 64k (I don't care how). > > > >> > >>>>>>>> sockopt = the setsockopt mechanism > >>>>>>>> val = the value assigned in default or via setsockopt > >>>>>>>> sk_buf = short for sk_{snd|rcv}buf > >>>>>>>> real_buf = the real size of the buffer (sk_buf_size in __smc_buf_create) > >>>>>>>> > >>>>>>>> exposed | net/core/sock.c | af_smc.c | smc_core.c > >>>>>>>> | | | > >>>>>>>> +---------+ | | +------------+ | +-------------------+ > >>>>>>>> | default |----------------------| sk_buf=val |---| real_buf=sk_buf/2 | > >>>>>>>> +---------+ | | +------------+ | +-------------------+ > >>>>>>>> | | | ^ > >>>>>>>> | | | | > >>>>>>>> +---------+ | +--------------+ | | | > >>>>>>>> | sockopt |---| sk_buf=val*2 |-----------------------| > >>>>>>>> +---------+ | +--------------+ | | > >>>>>>>> | | | > >>>>>>>> > >>>>>>>> The fixed patch introduced a dedicated sysctl for smc > >>>>>>>> and removed the /2 in smc_core.c resulting in the following flow: > >>>>>>>> > >>>>>>>> default = net.smc.{w|r}mem (which defaults to net.ipv4.tcp_{w|r}mem[1]) > >>>>>>>> sockopt = the setsockopt mechanism > >>>>>>>> val = the value assigned in default or via setsockopt > >>>>>>>> sk_buf = short for sk_{snd|rcv}buf > >>>>>>>> real_buf = the real size of the buffer (sk_buf_size in __smc_buf_create) > >>>>>>>> > >>>>>>>> exposed | net/core/sock.c | af_smc.c | smc_core.c > >>>>>>>> | | | > >>>>>>>> +---------+ | | +------------+ | +-----------------+ > >>>>>>>> | default |----------------------| sk_buf=val |---| real_buf=sk_buf | > >>>>>>>> +---------+ | | +------------+ | +-----------------+ > >>>>>>>> | | | ^ > >>>>>>>> | | | | > >>>>>>>> +---------+ | +--------------+ | | | > >>>>>>>> | sockopt |---| sk_buf=val*2 |-----------------------| > >>>>>>>> +---------+ | +--------------+ | | > >>>>>>>> | | | > >>>>>>>> > >>>>>>>> This would result in double of memory used for existing configurations > >>>>>>>> that are using setsockopt. > >>>>>>> > >>>>>>> Firstly, thanks for your detailed diagrams :-) > >>>>>>> > >>>>>>> And the original decision to use user-provided values rather than > >>>>>>> value/2 to follow the instructions of the socket manual [1]. > >>>>>>> > >>>>>>> SO_RCVBUF > >>>>>>> Sets or gets the maximum socket receive buffer in bytes. > >>>>>>> The kernel doubles this value (to allow space for > >>>>>>> bookkeeping overhead) when it is set using setsockopt(2), > >>>>>>> and this doubled value is returned by getsockopt(2). The > >>>>>>> default value is set by the > >>>>>>> /proc/sys/net/core/rmem_default file, and the maximum > >>>>>>> allowed value is set by the /proc/sys/net/core/rmem_max > >>>>>>> file. The minimum (doubled) value for this option is 256. > >>>>>>> > >>>>>>> [1] https://man7.org/linux/man-pages/man7/socket.7.html > >>>>>>> > >>>>>>> The user of SMC should know that setsockopt() with SO_{RCV|SND}BUF will > >>>>>> > >>>>>> I totally agree that an educated user of SMC should know about that behavior > >>>>>> if they decide to use it. > >>>>>> We do provide our users preload libraries where they can pass preferred > >>>>>> buffersizes via arguments and we handle the Sockopts for them. > >>>>>> > >>>>>>> double the values in kernel, and getsockopt() will return the doubled > >>>>>>> values. So that they should use half of the values which are passed to > >>>>>>> setsockopt(). The original patch tries to make things easier in SMC and > >>>>>>> let user-space to handle them following the socket manual. > >>>>>>> > >>>>>>>> SMC historically decided to use the explicit value given by the user > >>>>>>>> to allocate the memory. This is why we used the /2 in smc_core.c. > >>>>>>>> That logic was not applied to the default value. > >>>>>>> > >>>>>>> Yep, let back to the patch which introduced smc_{w|r}mem knobs, it's a > >>>>>>> trade-off to follow original logic of SMC, or follow the socket manual. > >>>>>>> We decides to follow the instruction of manuals in the end. > >>>>>> > >>>>>> I understand the point. I spend a lot of time trying to decide what to do. > >>>>>> > >>>>>> Since it was an intentional decision to not follow the general socket > >>>>>> option, and we do not have anyone complaining we do not really have a reason > >>>>>> to change it. > >>>>>> Changing it means that users with existing configurations would have to > >>>>>> change their configs on an update or suddenly expect double the memory > >>>>>> consumption. > >>>>>> That's why we in the end preffered to stay with the current logic. > >>>>> > >>>>> I can't agree with you more with the points to follow the historic logic > >>>>> and not break the user-space applications. > >>>>> > >>>>>> I'm thinking that maybe - if we stay with the historic logic - we should > >>>>>> document that desicion somewhere. So that in the future, if a user that > >>>>>> expects the man page behavior, has a way to understand what SMC is doing. > >>>>>> What do oyu think? > >>>>> > >>>>> Yep, we _really_ need to document it if we change the convention. > >>>>> Actually, I spent a lot of time to find the history about the logic of > >>>>> buffer (/2 and *2) in SMC. So I'm really in favor of adding > >>>>> documentation, at least code comments to help others to understand them. > >>>>> > >>>>> Cheers, > >>>>> Tony Lu > >>>> 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 > >>> see above: send: 16k 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) > >>> See above, I stand corrected. However this patch fixes/restores the buffersize > >>> for setsockopt, but not for the default recieve path. > >>> Could you please clarify that in the title and description? > >>> > >> > >> I am trying to keep the commit title as crisp as possible while providing > >> enough information and set the context in the commit message: > >> > >> "The fixed commit changed the expected behavior of buffersizes set by the > >> user using the setsockopt mechanism." > >> > >> + There is now a whole e-mail thread to consult in case of any further > >> questions. > >> > >> Thank you for your comments > >> - Jan > >> > >>> Reviewed-by: Alexandra Winter <wintera@...ux.ibm.com> > >>>>>> - Jan > >>>>>> > >>>>>>> > >>>>>>> Cheers, > >>>>>>> Tony Lu > >>>>>>> > >>>>>>>> Since we now have our own sysctl, which is also exposed to the user, > >>>>>>>> we should sync the logic in a way that both values are the real value > >>>>>>>> used by our code and shown by smc_stats. To achieve this this patch > >>>>>>>> changes the behavior to: > >>>>>>>> > >>>>>>>> default = net.smc.{w|r}mem (which defaults to net.ipv4.tcp_{w|r}mem[1]) > >>>>>>>> sockopt = the setsockopt mechanism > >>>>>>>> val = the value assigned in default or via setsockopt > >>>>>>>> sk_buf = short for sk_{snd|rcv}buf > >>>>>>>> real_buf = the real size of the buffer (sk_buf_size in __smc_buf_create) > >>>>>>>> > >>>>>>>> exposed | net/core/sock.c | af_smc.c | smc_core.c > >>>>>>>> | | | > >>>>>>>> +---------+ | | +-------------+ | +-----------------+ > >>>>>>>> | default |----------------------| sk_buf=val*2|---|real_buf=sk_buf/2| > >>>>>>>> +---------+ | | +-------------+ | +-----------------+ > >>>>>>>> | | | ^ > >>>>>>>> | | | | > >>>>>>>> +---------+ | +--------------+ | | | > >>>>>>>> | sockopt |---| sk_buf=val*2 |------------------------| > >>>>>>>> +---------+ | +--------------+ | | > >>>>>>>> | | | > >>>>>>>> > >>>>>>>> This way both paths follow the same pattern and the expected behavior > >>>>>>>> is re-established. > >>>>>>>> > >>>>>>>> Fixes: 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable") > >>>>>>>> Signed-off-by: Jan Karcher <jaka@...ux.ibm.com> > >>>>>>>> Reviewed-by: Wenjia Zhang <wenjia@...ux.ibm.com> > >>>>>>>> --- > >>>>>>>> net/smc/af_smc.c | 9 +++++++-- > >>>>>>>> net/smc/smc_core.c | 8 ++++---- > >>>>>>>> 2 files changed, 11 insertions(+), 6 deletions(-) > >>>>>>>> > >>>>>>>> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c > >>>>>>>> index 036532cf39aa..a8c84e7bac99 100644 > >>>>>>>> --- a/net/smc/af_smc.c > >>>>>>>> +++ b/net/smc/af_smc.c > >>>>>>>> @@ -366,6 +366,7 @@ static void smc_destruct(struct sock *sk) > >>>>>>>> static struct sock *smc_sock_alloc(struct net *net, struct socket *sock, > >>>>>>>> int protocol) > >>>>>>>> { > >>>>>>>> + int buffersize_without_overhead; > >>>>>>>> struct smc_sock *smc; > >>>>>>>> struct proto *prot; > >>>>>>>> struct sock *sk; > >>>>>>>> @@ -379,8 +380,12 @@ static struct sock *smc_sock_alloc(struct net *net, struct socket *sock, > >>>>>>>> sk->sk_state = SMC_INIT; > >>>>>>>> sk->sk_destruct = smc_destruct; > >>>>>>>> sk->sk_protocol = protocol; > >>>>>>>> - WRITE_ONCE(sk->sk_sndbuf, READ_ONCE(net->smc.sysctl_wmem)); > >>>>>>>> - WRITE_ONCE(sk->sk_rcvbuf, READ_ONCE(net->smc.sysctl_rmem)); > >>>>>>>> + buffersize_without_overhead = > >>>>>>>> + min_t(int, READ_ONCE(net->smc.sysctl_wmem), INT_MAX / 2); > >>>>>>>> + WRITE_ONCE(sk->sk_sndbuf, buffersize_without_overhead * 2); > >>>>>>>> + buffersize_without_overhead = > >>>>>>>> + min_t(int, READ_ONCE(net->smc.sysctl_rmem), INT_MAX / 2); > >>>>>>>> + WRITE_ONCE(sk->sk_rcvbuf, buffersize_without_overhead * 2); > >>>>>>>> smc = smc_sk(sk); > >>>>>>>> INIT_WORK(&smc->tcp_listen_work, smc_tcp_listen_work); > >>>>>>>> INIT_WORK(&smc->connect_work, smc_connect_work); > >>>>>>>> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c > >>>>>>>> index 00fb352c2765..36850a2ae167 100644 > >>>>>>>> --- a/net/smc/smc_core.c > >>>>>>>> +++ b/net/smc/smc_core.c > >>>>>>>> @@ -2314,10 +2314,10 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb) > >>>>>>>> if (is_rmb) > >>>>>>>> /* use socket recv buffer size (w/o overhead) as start value */ > >>>>>>>> - sk_buf_size = smc->sk.sk_rcvbuf; > >>>>>>>> + sk_buf_size = smc->sk.sk_rcvbuf / 2; > >>>>>>>> else > >>>>>>>> /* use socket send buffer size (w/o overhead) as start value */ > >>>>>>>> - sk_buf_size = smc->sk.sk_sndbuf; > >>>>>>>> + sk_buf_size = smc->sk.sk_sndbuf / 2; > >>>>>>>> for (bufsize_short = smc_compress_bufsize(sk_buf_size, is_smcd, is_rmb); > >>>>>>>> bufsize_short >= 0; bufsize_short--) { > >>>>>>>> @@ -2376,7 +2376,7 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb) > >>>>>>>> if (is_rmb) { > >>>>>>>> conn->rmb_desc = buf_desc; > >>>>>>>> conn->rmbe_size_short = bufsize_short; > >>>>>>>> - smc->sk.sk_rcvbuf = bufsize; > >>>>>>>> + smc->sk.sk_rcvbuf = bufsize * 2; > >>>>>>>> atomic_set(&conn->bytes_to_rcv, 0); > >>>>>>>> conn->rmbe_update_limit = > >>>>>>>> smc_rmb_wnd_update_limit(buf_desc->len); > >>>>>>>> @@ -2384,7 +2384,7 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb) > >>>>>>>> smc_ism_set_conn(conn); /* map RMB/smcd_dev to conn */ > >>>>>>>> } else { > >>>>>>>> conn->sndbuf_desc = buf_desc; > >>>>>>>> - smc->sk.sk_sndbuf = bufsize; > >>>>>>>> + smc->sk.sk_sndbuf = bufsize * 2; > >>>>>>>> atomic_set(&conn->sndbuf_space, bufsize); > >>>>>>>> } > >>>>>>>> return 0; > >>>>>>>> -- > >>>>>>>> 2.34.1
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